Leog

I don't know these new round displays well. But all these displays work much the same: there is a long serial data stream sent to them at high speed (SPI or I²C I think). Typically there will be three wires for this serial bus: ground, data, and clock. I believe that the round display is actually two or three of these displays; it looks like it's just the lower one playing up on your inverter. I would find these cables, take them out and re-insert several times, and/or squirt with something like CRC contact cleaner (NOTE: nothing that's oily and would leave a residue).  Also look for damaged wires, repair or replace as needed.
If this doesn't fix things, the other thing that happens is that the conductive rubber block that connects the transparent but conductive traces on the display glass to the display PCB can move out of place, or not make proper contact. These things conduct from top to bottom but not side to side. Fiddle as required. This repair probably requires more things to be taken apart, so leave this one last.
Of course, you could also return it under warranty, but at this time of year, that could take a long time, plus repair facilities will be overloaded with inverters boxes with bad lead acid batteries, from all the load shedding.
Good luck. 
Edit: It seems to be a known issue; see this post below.

These are EVE LF105 cells, Grade A as per Seller (Nkon is reputable europe battery seller)
I torqued with hand. Toughest was the small screws that bolt on the cells. These are miniature philips head.
Had to buy a hydraulic press for the fittings as it gives me peace of mind on the connections.
Also added plastic sheets in between the cells for added protection. 
Compressed only by some duct tape, not going the heavy compression route.
Battery went into heavy duty plastic box with lid. Wiring is 4awg with 160A NH00 Fuse.
The bms is the JK-BMS 100A version with bluetooth and 0.6A balancer integrated.
The app in my phone is awesome and i see everything i need for the battery.
Tested with my Uni-T210E bms is accurate.

I do see the first cell always being an outlier  , it just keeps having lower voltage. And the balancer keeps propping it up.
In theory with bulk charging at 56v and float at 55v i wont see ever the OVP bms protection kick in as it is at 3,65v (58.4v).


Nice thing about this BMS, you can put the battery connection without sparks or the need to precharge.
Once you have everything wired up you can enable discharge from the app!
 

These are EVE LF105 cells, Grade A as per Seller (Nkon is reputable europe battery seller)
I torqued with hand. Toughest was the small screws that bolt on the cells. These are miniature philips head.
Had to buy a hydraulic press for the fittings as it gives me peace of mind on the connections.
Also added plastic sheets in between the cells for added protection. 
Compressed only by some duct tape, not going the heavy compression route.
Battery went into heavy duty plastic box with lid. Wiring is 4awg with 160A NH00 Fuse.
The bms is the JK-BMS 100A version with bluetooth and 0.6A balancer integrated.
The app in my phone is awesome and i see everything i need for the battery.
Tested with my Uni-T210E bms is accurate.

I do see the first cell always being an outlier  , it just keeps having lower voltage. And the balancer keeps propping it up.
In theory with bulk charging at 56v and float at 55v i wont see ever the OVP bms protection kick in as it is at 3,65v (58.4v).


Nice thing about this BMS, you can put the battery connection without sparks or the need to precharge.
Once you have everything wired up you can enable discharge from the app!
 

Writing a summary here for helping others on the baterryless feature of the MKS IV.
It doesn't start immediately, beeps sometimes and if you leave it with load for 2-3 min it starts giving output ( no clue why this happens). With around 210v indeed its working batteryless together with AC IN fine. Went through the night with inverter going into bypass mode essentially providing the load from ac in completely. (average consumption of inverter around 50w), in the morning mppt engaged fine on its own. When PV is available it does have a minimum threshold of ac and pv it mixes. If the load is low < 300w (haven't found exactly) then around 220-240w come from the AC IN and rest from the PV. As soon as you put a 1000-2000w load then PV engages and ac IN load goes down to 100-150w and rest comes from PV. Load surges are first being supported by AC IN until mppt ramps up, then the load transfers to PV. Takes about 3-4seconds No lights are flickering nor other issues for now. My whole house is almost** supplied by the Axpert.

  Will come back after some time to report if running it batteryless has any impact at all overall.



** Except ceramic stove, well pump and heat geysers ( i have gas heater)

Writing a summary here for helping others on the baterryless feature of the MKS IV.
It doesn't start immediately, beeps sometimes and if you leave it with load for 2-3 min it starts giving output ( no clue why this happens). With around 210v indeed its working batteryless together with AC IN fine. Went through the night with inverter going into bypass mode essentially providing the load from ac in completely. (average consumption of inverter around 50w), in the morning mppt engaged fine on its own. When PV is available it does have a minimum threshold of ac and pv it mixes. If the load is low < 300w (haven't found exactly) then around 220-240w come from the AC IN and rest from the PV. As soon as you put a 1000-2000w load then PV engages and ac IN load goes down to 100-150w and rest comes from PV. Load surges are first being supported by AC IN until mppt ramps up, then the load transfers to PV. Takes about 3-4seconds No lights are flickering nor other issues for now. My whole house is almost** supplied by the Axpert.

  Will come back after some time to report if running it batteryless has any impact at all overall.



** Except ceramic stove, well pump and heat geysers ( i have gas heater)

Writing a summary here for helping others on the baterryless feature of the MKS IV.
It doesn't start immediately, beeps sometimes and if you leave it with load for 2-3 min it starts giving output ( no clue why this happens). With around 210v indeed its working batteryless together with AC IN fine. Went through the night with inverter going into bypass mode essentially providing the load from ac in completely. (average consumption of inverter around 50w), in the morning mppt engaged fine on its own. When PV is available it does have a minimum threshold of ac and pv it mixes. If the load is low < 300w (haven't found exactly) then around 220-240w come from the AC IN and rest from the PV. As soon as you put a 1000-2000w load then PV engages and ac IN load goes down to 100-150w and rest comes from PV. Load surges are first being supported by AC IN until mppt ramps up, then the load transfers to PV. Takes about 3-4seconds No lights are flickering nor other issues for now. My whole house is almost** supplied by the Axpert.

  Will come back after some time to report if running it batteryless has any impact at all overall.



** Except ceramic stove, well pump and heat geysers ( i have gas heater)

Give this man a Bells!!! You got there in the end. 

Writing a summary here for helping others on the baterryless feature of the MKS IV.
It doesn't start immediately, beeps sometimes and if you leave it with load for 2-3 min it starts giving output ( no clue why this happens). With around 210v indeed its working batteryless together with AC IN fine. Went through the night with inverter going into bypass mode essentially providing the load from ac in completely. (average consumption of inverter around 50w), in the morning mppt engaged fine on its own. When PV is available it does have a minimum threshold of ac and pv it mixes. If the load is low < 300w (haven't found exactly) then around 220-240w come from the AC IN and rest from the PV. As soon as you put a 1000-2000w load then PV engages and ac IN load goes down to 100-150w and rest comes from PV. Load surges are first being supported by AC IN until mppt ramps up, then the load transfers to PV. Takes about 3-4seconds No lights are flickering nor other issues for now. My whole house is almost** supplied by the Axpert.

  Will come back after some time to report if running it batteryless has any impact at all overall.



** Except ceramic stove, well pump and heat geysers ( i have gas heater)

Exactly what i did, i have in total 4 surge arrestors in my whole setup just to make sure the inverter is not exposed to unsafe voltage spikes that will shorten its lifespan.
2 in the ac IN (house-inverter), 1 in ac out and 1 in dc. 
Not sure this would be enough for an axpert though.