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Regarding the Pylontech firmware...  First up, thanks for this thread.  It is without doubt the most useful resource on the internet relating to the issues discussed.
So... I had the issue with the Victron GX + <v1.7 f/w on a couple of my US3000Cs - the misreporting of a voltage spike in one cell causing the Victron GX to panic and shut that battery down.
I emailed Pylontech with a plot of the Vhigh readings (it would shoot to 4.1v for one reading, then back down again).  They responded very promptly (on a Sunday night, too) with a link to download a zip containing 'BatteryView 3.0.33' and a firmware zip file named 'USC_st2.8+NT2.2.zip', contained two binaries named 'US_E2_V2.2_Crc.bin' and 'US_C_V2.8_Crc.bin'.  Good so far.
Then the real fun started...
Couldn't get 'BatteryView' to connect, despite no problems accessing the serial terminal and getting appropriate responses from the batteries.
Tried 'Batteryview' under wine/mono in Linux Mint 21, build a Windows 10 VM, fully updated it, installed Win 10 natively, updated that, .NET 4.8.1, tried every combination of v 3.0.28 through 3.0.33, 3 different USB/RS232 interfaces...  Wouldn't connect, but terminal was fine.
Eventually did a native install of Win 11, same deal... Updated that (which took the best part of a day on a 40Mb/s fibre line) and finally, finally 'BatteryView' connected.  Downloaded all the 'history' and 'event' data, went to update the firmware on the first battery (according to the instructions provided by Pylontech, using the zip file) and...   it threw an 'unknown exception' error and just quit. 😭
OK.
Took a step back, sat down with a cup of tea and thought 'lets have a look at this firmware zip file'.  The one that 'thou shalt not unzip, least ye bricketh the unit'.  Re-read this thread, then thought that if I can work out which of the two bin files, maybe try that?  I mean, who's gonna know, right?
And lo, it came to pass that I could not unzippeth.  Because the %&*$!£ zip-within-the-zip was corrupt.  Re-downloaded from the source (wetransfer.com), same.
Came back here and grabbed the v1.8 zip, all 7 units are now updated fine. 🥳
 
So basically, a massive 'Thank You' to Youda and all who have contributed to this thread.  I hope the above contribution to it might prove useful to someone else facing similar issues.
Now I can hopefully sleep easy, or at least sleep without VRM waking me up with an email at 3.23am to inform me in panicked, breathless tones of some expensive-sounding 'internal failure' or 'cell imbalance' in battery 7 that means you have to get up and shuffle downstairs to silence the beep-of-doom and check that nothing's actually on fire. 🙂