There is no point to convert MP3 files to FLAC. You will not restore any of the lost data, you will only end up with larger files.
It would be good to convert WAV to FLAC. The FLAC files will be smaller than the WAV files, and there will be no information lost.
Given your current situation, I would leave the FLAC and MP3 files as they are. However, I would try to find a way to convert the WAV files to FLAC. If the B2 is stuck and cannot convert those 19 WAV files, copy them to a USB disk and do the conversion on your computer.