That's one way around it, I suppose, @Lieutenant_Lars1967. But I don't trust myself to get it right the first time, especially 'at the last minute'!
I backed up the new installation and then deleted everything related to OpenLP. I then reinstalled a clean '2.9.4', and everything seems to be working correctly.
When Raoul and the team have the time and have figured out the problem, we'll get a fix. In the meantime, I'm grateful for the software and for not having to use PowerPoint (or similar) to do things that they were never designed to do!