[itsme]

I assume you restored my backup. Could you reproduce the issue that I reported?

The files that showed the issue are  "557 Standards.PDF", "HLJPA-028 – Big Band Era.pdf" and "Liedler.pdf"
Songs named  "557 Standards", "HLJPA-028 – Big Band Era" and "Liedler" do NOT exist in my library. These files are fakebooks containing songs with completely different names. The most similar song names are e.g. "~557 Standards C – TOC", "~557 Standards C (complete)". But that's my naming scheme for all my fakebooks, not only for the three affected ones. The one and only song using "HLJPA-028 – Big Band Era.pdf" is "Christopher Columbus". I don't see any case where "the relative path starts with <song title>/file.pdf".
What's identical is the filename and the foldername, but that's also the case for many other fakebooks e.g. RealBookOfBlues.pdf, BluegrassFakebook.pdf, BuskItCountry.pdf and many others.

So your explanation doesn't match the issue I'm facing. Nevertheless I'll pick up your hint and experiment with changing the foldernames for the affected fakebook files and see what happens.