Try to use Electrum v4.3.2 if the issue will persist.

If not, it may have something to do with this Commit: https://github.com/spesmilo/electrum/commit/d3227d7489fe327bd40e891a517c86bd207227ec (in v4.3.3)

If still there, enable logging and check if it has something that's related to the error.
You can enable logging in "Tools->Preferences->Misc->Write logs to file" (restart Electrum), reproduce the error and then disable logging.
Log is in "logs" folder in Electrum's datadir (location).