Sometimes when I use the Table editor to change the columns on a table I get the following error:

There seems to be no obvious pattern and the Statements Log doesn't contain anything obvious.
Once that has happened I basically have to close down my connection (losing any uncommitted changes)
I don't get any errors anywhere else - its only when I use the Table Editor.
This is in Version 4.1.0.19 Build MAIN-19.07