The_Duk3_

@cp69 Thanks, glad to hear the information has been useful. I have no desire to be a brand ambassador though, just trying to be objective and hopefully that's useful to others.
On to some other info.
- While I was busy discharging my batteries to get them below the minimum settable battery SoC for the generator to be usable (90%), I had a substantial load running on the inverter for about 45 minutes, that included my geyser, aircons and an electric hob plate or two. I noted the inverter internal fan was switching on when the load was higher than 3kw and off below that. Here is a graph of the load and resulting internal temperature,y which peaked at just over 57 deg.C. Generally the temperature tends to sit at between 30 and 35 deg.C.

- There is an interesting issue with the Solis app where if you have no Internet access, you can't seem to connect to the device locally to configure it. I tried a few times of restarting the app and waiting a fair while but it gets stuck on the screen below. Easy enough to get around with a mobile data connection via your phone, but still somewhat bizarre to require an Internet connection to perform local Bluetooth configuration.

- The inverter is currently connected to Pylontech batteries and I wanted to test it with a Greenrich battery, which I have been told by Greenrich is compatible the Pylontech BMS protocol. As I didn't see it listed in the settings area for batteries, I simply left the inverter in the Pylontech setting and the BMS worked perfectly with the greenrich battery. However, the inverter didn't want to enable the load output and on investigation I could see there was some strange bus voltage alarm. After reviewing the battery parameters displayed by the inverter, I could see the high voltage charge protection value I had previously set to 53v for the Pylontech was probably the issue as the Greenrich was already above that value. However, I could not find the setting anywhere in the settings menu indicating it was probably removed at some point. I eventually ran the Quick Setup again which actually has a much longer list of supported batteries (including Greenrich) than the settings menu where I was looking. Here's the current list. I suspect Hubble batteries will also work with the Pylontech setting.

Here is another snapshot. Running SBU from 10:26 with much greater loads(upto 8kW), hotter ambient temperatures and PV power close to 5kW, and the inverter didn't move once over 60C. It just seems like the SUB mode is flawed.  I will run a test tonight in SUB more and see if there is still the same issue without solar production. 

Thanks @Steve87 and  @WannabeSolarSparky . Please find the pic of the setup attached. 
Awesome thanks @WannabeSolarSparky good to know. Any reason why we don't see the same temperatures when it is running in SBU. Is the AC-AC with solar DC-AC really that inefficient. It seems like the DC-AC only is a lot more efficient. 
Could the losses have something to do with synchronizing with the grid?  

Hi Power forum,
First time poster here. Recently installed an RCT AXPERT MAX 8KVA/8KW with 3x pylontech US300C batteries and 18x395w Jinko panes (2 strings 10/8). Everything is running well, except for some strange issues with regard to "Blended" power from Solar/Grid Mode. I am seeing inverter temperatures above 70C. The inverter is located undercover with ample air at cool winter temperatures <20C. 
Has anyone else seen issues like this with their inverters? 
Iv added a picture of todays test although this happens every time the inverter goes into Solar/Grid Mode. As soon as I manually change it to Solar/Battery mode temps get much better. 
Any insights would be great. The inverter is ~1 month old. 

Good Day All
Just a quick update.
I've decided to go for the Greenrich WM5000 instead and so far I'm very happy with my purchase and thanks to all of your advise and guidance with the decision as well.
I also want to say thank you for @GerhardK83 and @Gustav du Plessis for sharing the cable pinouts and I can confirm that it does connect with no issues at all.

Thank you for the recommendation. I will also add this to my list of batteries.

This is a wild gamble, but I have read your post and have a theory, these inverters, well the older ones like mine have a bypass enable and disable setting, it somehow decides that when drawing too much current from the batteries, to protect it it bypasses, my theory is that this is what is causing yours to do this, and this setting is based on your charging current to the batteries, so I think if you were to set this to a high value it might not do this. But then you risk the battery. 
The guys who know the firmware might know how these calculations are done.

Unfortunately, I don't know of any 46.xx firmware update files. However, I've just uploaded version 90.06, which is only a few weeks old. Being a 90.xx version, it may be experimental, though it seems from other posts that they are being treated as production firmware.
There is also removable display firmware version 12.11 somewhere, but that doesn't seem to be related to your issues. Use at your own risk.

Now here:
 

Do you mean it switches between battery mode (battery and solar powering loads) and line mode (line, battery, and solar powering loads)? Or do you actually see SBU and SUB on your monitoring software?
Buggy firmware is a possibility. What is your main (U1) firmware version?
A faulty unit is possible, but seems much less likely.