Thanks very much for all the help.
This was my exact suspicion, that it’s Onedrive not catching up with how fast darktable is writing to the xmp files. The error does some to happen when I’m working particularly fast and making lots of quick changes (like turning modules on and off, etc.). It’s strange that I never noticed it before with builds prior to 3.4, but I can’t imagine that the xmp write frequency has changed…
It’s an annoyance, but as you @priort have also noticed, it doesn’t seem to cause any long-term issues. On balance, I think it’s worth living with rather than relocating my files and not having Onedrive sync them. I love the automatic backup to ensure I never lose anything.
If anyone has any ideas for how to “fix” it, please shout out. Is it just coincidence that I’m only seeing this since build 3.4? @priort did you notice it before?