FLAC files getting corrupted on microSD card Whenever I put a FLAC album on my phone, after a few days some of the tracks get corrupted. They show errors when I bring them onto my PC and use the command line function flac -t *.flac. While most tracks result in an ok, some result in errors such as FLAC__STREAM_DECODER_ERROR_STATUS_LOST_SYNC or FLAC__STREAM_DECODER_ERROR_STATUS_FRAME_CRC_MISMATCH. I am using LineageOS 15.1 (July 23 build) on my SM-G900P with a genuine SanDisk 128GB Extreme PLUS microSD card formatted as adopted/internal storage. I read somewhere about a LOST.DIR folder being used as a recycling bin for corrupted files or something like that, but I don't seem to have that folder.

Is this an issue with Samsung, Android, LineageOS, Poweramp (my music player), or my SD card? I really hope it's not an SD card issue because I don't feel like spending so much time formatting/moving a ton of data around.

Thanks.
This is almost certainly an SD card issue, especially since initially the files are fine and not corrupt, and get that way over time. Your device and it's applications will only read the data from the SD card, not change it or write to it anyway. There is a very slim chance that the card reader in your phone is defective, but I think a safe bet would be the card itself is failing. 

This is the most definitive answer I can offer with the information given. 

I am not normally one to recommend a specific brand here, but my personal experience with SanDisk has been very disappointing in terms of reliability in multiple product lines they carry. I would recommend moving away from SanDisk and trying perhaps a Samsung EVO+ series card.