Chass90

This is a beta version of the patched firmware version 71.80a, based on factory firmware version 71.80 for Axpert MKS II 5K-48, PIP-5048MG, and equivalents. It is not to be confused with factory firmware version 71.80 for the Axpert King and PIP-5048MK. The only changes are that the two premature float bugs are fixed, and the version number on the LC Display is different.
71.80a (and 71.80) should be direct update replacements for firmware versions 71.70 and 71.71. However, 71.80 handles 4 extra CAN commands, so it is probably wise to update all paralleled / 3-phase machines at once. 71.80 has unannounced and undocumented new BMS features; see this post. New ^DnnnBMS command documented (by me) here.
This is untested apart from disassembling the patches. As always, use at your own risk.
File and download instructions here: https://forums.aeva.asn.au/viewtopic.php?p=78818#p78818

When the panels are disconnected in this state, there is a voltage of about 50V at the panel connector on the inverter.  I am going to insert a diode between the panels and the inverter and see if it makes any difference...
 

Here is something extremely interesting!!!
The inverter currently is in its bad mood.  When you switch it off at the bottom, the bus voltage goes to zero.  When you switch it on again, the voltage quickly goes to 380V and then rises quite fast until it trips.  Out of sheer curiosity / desperation, I switched off the solar panels.  The bus voltage dropped to 380V in a matter of 30s!!!  Now remember - the unit is in bypass.  It is pitch dark outside.  I have measured the solar panel input - just about 0V.  So why the heck would removing the panels, "solve" the problem???

My initial thought was that they had ported the PylonTech battery type == PYL code to this machine. [ Edit: That is, the Axpert MKS II. ] Alas, no.
There is a new command QBMS, which spits out data like BMS battery voltage, maximum charge current, and so on.
This information comes from parsing a new command of the form ^DnnnBMSddd... where nnn is the length of the command, just like a device response from a "secure" command (ones that start with the up-arrow). This seems to use the serial port that is otherwise unused in these models with 450 V max Solar Charge Controllers. That serial port is used to talk to the processor on the Solar Charge Controller in 145 V max SCC models; in the 450 V max SCC models, the DSP controls the PV boost converter directly, and so doesn't need the second serial port.
The maximum charge current value (and likely other values) seems to be actually used; in the case of maximum charge current, it is used instead of the EEPROM maximum charge current setting, if appropriate bits are set. Presumably those bits indicate that the BMS is connected and BMS data is actively being received.
I note that the Pylontech BMS information is in a packet that starts with an up-arrow, but as far as I can tell, the format is different. So this is not directly for PylonTechs. So what is it for? A great question. My wild guess is that Voltronic Power are developing some new interface for battery BMSs, separate from the inverter-chargers themselves, which might translate BMS data from various different battery BMSs into one format, the one indicated above. But I stress that this is a wild guess. I'm further guessing that it's not quite ready yet, but the firmware source code is in the process of incorporating this new functionality, and when a fix for the bus voltage control / error 08 bug was needed, this BMS stuff "came along for the ride".
So while this new BMS code isn't a port of the battery type == PYL code, it might even be something better.
As for what they changed in the way of bus voltage control, I've not found that code as yet. There are plenty of red herrings: variables and functions with "busv" in the name, but aren't used. I may get to it tomorrow my time; I'm curious as to what they've done. With all the BMS code additions, it's not a simple matter of comparing function lengths to see where significant changes have occurred.
Edit 29 June 2020: this command may have been experimental, or have vastly evolved, as noted in this post.

I did put up a fuss with Voltronic themselves regardings this issue.  At first they gave me a lame answer as follows :
"Per your information below, it means error 08 was caused by the surge from the grid input. Error 08 means high BUS voltage, if the grid is not stable, and has high voltage spike, it will make the inverter BUS over voltage, then error 08 will happen.
 The inverter will restart when Error 08 happened. But the bus voltage must be lower than 500V. It can restart three times within 15 minutes.  If it exceeds three times, it won’t restart automatically. You will need to turn off the power and restart the inverter manually."
 I told them that the answer was not good enough since we have surge suppression installed and that the grid voltage was 223Vac at the time when the error appeared
I then received the following answer :
"Our RD has prepared updated firmware to improve error 08. Please find the download link below. The password is “daily”.  
 Please upgrade the firmware and check whether error 08 is resolved. "
I hope I achieved progress for all of us
AxpertMKSII5K71.80P.rar