Okay, I found two comparable files:
The first has incompatible encoding according to the readout.
Entry "/Elias Doré/Elias Doré @ Rebellion der Träumer, 07.05.16_263237326 - Elias Doré.mp3" will not be accessible due to incompatible encoding
strace shows
lstat64("Elias Dore\314\201 @ Rebellion der Tra\314\210umer, 07.05.16_263237326 - Elias Dor\303\251.mp3", {st_mode=S_IFREG|0777, st_size=178917458, ...}) = 0
But this one throws no error:
File /Elias Doré/Bucht der Träumer 2019 - Atlantis, Friday Night_668487995 - Elias Doré.mp3
lstat64("Bucht der Tr\303\244umer 2019 - Atlantis, Friday Night_668487995 - Elias Dor\303\251.mp3", {st_mode=S_IFREG|0777, st_size=169984834, ...}) = 0
Can anyone read this fluently? I have very little experience with weird encoding errors.