Hello,
The issue most likely stems from the configuration not being transferred correctly from the older firmware version and a factory reset might be the best option. If the issue still persists, I'd recommend performing a factory reset using the bootloader method, which will completely reflash the OS and should get rid of any instability.
Please also keep in mind, that logouts from the WebUI when the tab is left open but not interacted with is the intended behavior, but this should only happen after around 10 minutes of inactivity, and not while using the WebUI.
Best regards,
DaumantasG