I think I might know what the problem is, i.e. I have two copies of the core running on the same PC: one as a Roon Server and one as a Roon App.
The problem above occurs because my phone can’t always find the correct version of the core.
I don’t think there is much value in Roon Support chasing down these now, non-existent, problems, so let’s close this topic and continue in this new one.