(Sorry for the hassle!)
Short update after talking to Armin and diagnosing further with the team: we are still uncertain why the problem occurs, but we now have a recipe to reproduce it – at least on Windows. Updating older KNIME installations is part of our testing protocol and did not fail in our release testing.
We haven’t been able to fully understand the issue, but we’re continuing to diagnose it. For now, if you encounter the problem, you can work around it by adding -clean to the knime.ini file above the -vmargs line. This line can be removed after KNIME has started. Alternatively, you can start KNIME from the command line with -clean as an argument.
We’ll keep this thread updated as we find out more details.