I was updating the tags of Wavpack files (wv) with 'rename' and 'move files' activated. I noticed afterwards that the Wavpack correction files (wvc) in the same folder were treated as duplicates and erroneously renamed with a ' (1).wv' ending.
I have only recently updated picard from 1.4.2 (Ubuntu universe package) to the current stable snap version, so this problem might have existed for some time now.
No files were lost, but the correction files needed to be renamed manually. Otherwise the data in the wvc files would not be included when decoding the wv files.
D: 14:04:52,365 /snap/picard/760/lib/python3.8/site-packages/picard/file._rename:512: Moving file '/media/surium/Audio/Musiksammlung/Scala & Kolacny Brothers/One-Winged Angel/01. Joga.wvc' => '/media/surium/Audio/Musiksammlung/Scala & Kolacny Brothers/One-Winged Angel/01. Joga (1).wv'D: 14:04:52,365 /snap/picard/760/lib/python3.8/site-packages/picard/formats/apev2._save:186: Saving file '/media/surium/Audio/Musiksammlung/Scala & Kolacny Brothers/One-Winged Angel/01. Joga.wv'D: 14:04:52,386 /snap/picard/760/lib/python3.8/site-packages/picard/file._save_and_rename:350: Not removing empty directory: /media/surium/Audio/Musiksammlung/Scala & Kolacny Brothers/One-Winged Angel is not emptyD: 14:04:52,386 /snap/picard/760/lib/python3.8/site-packages/picard/coverart/image.save:315: Using default cover image filename 'cover'D: 14:04:52,387 /snap/picard/760/lib/python3.8/site-packages/picard/coverart/image._is_write_needed:351: Identical file size, not saving b'/media/surium/Audio/Musiksammlung/Scala & Kolacny Brothers/One-Winged Angel/cover.jpg'D: 14:04:52,399 /snap/picard/760/lib/python3.8/site-packages/picard/file.update:665: Updating file <WavPackFile '01. Joga.wv'>