Can't sync: "1% and 1 other file can't be synced"

I attach the photo because this is a repeating error,
for sure caused by a strange filename that I can’t find.

I write “for sure” because this was happening also with owncloud,
and we didn’t migrate (we started from zero and reuploaded everything).
We have both Windows and Mac with NextCloud, I suspect the cause is a file with a strange character in the name caused by the Mac computer.

BUT, I can’t find any “1%”, can you help me to find it ?

I forgot to insert an image previously, here it is:

Please check your logfile like the message tells you. Could also be that there is an issue with your setup. But the percent sign could be problematic because it might not be supported by all client file systems. Search your mac sync folder for such a file. If it is a temporary file of a program it might be hidden.

related issue:

I solved 3 years later with:
/Applications/ --logwindow
And searching for weird characters in my filenames.

Command found here: