alextechs

Hello, also chiming in here with a setup similar to what @runtimeassertion initially had (Axpert VM III TWIN 4kW, labeled as LPW-HY-4000VA).
It seems I was luckier as I have not encountered any issues during the flash process, so I'd like to share my experience.
U1: from 56.09 to 60.10
U2: from 25.06 to 25.15
Used software that came together with the firmware.
The process was roughly the following:
Disconnected everything, except battery Flashed U1 via USB cable Connected AC input + AC load (intermediate check) Disconnected AC input + AC load Flashed U2 via USB-to-RS232-serial adapter Disconnected everything (power off) Connected everything (battery, AC input, AC load, PV input) Do not use this as a sole guide, please refer to https://powerforum.co.za/topic/29708-collection-of-dsp-axpert-firmware-for-vm-iii-twin-and-vm-iv-twin/  instead.
The newer firmware resolved the "stuck at 60V" issue for me. It's been more than a month since the upgrade without any new issues, so it can be considered successful.
I have not checked Wi-Fi connectivity as I abandoned it in favor of USB-to-RS232-serial adapter several months ago because Wi-Fi connection had to be reconfigured with each inverter power cycle and I wanted to stop relying on 3rd party cloud services anyway.
Hope this helps someone!
As always, huge thanks to @Coulomb for enabling others to perform inverter maintenance on their own.