Yes, all of the files that are now suspect were in a batch of about 80k files total changing any variation of "various artists" to "VA" (my preference) - this batch was over maybe 6 or 8 actions of searching, selecting, making change in vertical tag editor, click save.
I also did another batch yesterday using Regex Search and Replace (^[0]) on Track# to remove leading 0's yesterday that was closer to 150k tracks. I did notice a few odd files after that, but its after the above that I really noticed things going south.
Its definitely file corruption. It sounds the same in VLC via 2 different outputs.
Of all the files in the batch, only some (by far the minority) are affected. Some albums have one track corrupted, others have several. In one case an entire album was corrupted. The corruption amount varies wildly. The tags appear intact, but the album art is often missing or also corrupted. I have not re scanned the files yet.
I'm 100% sure they were fine beforehand, as I have either played it before or have gone to an older backup and the files sound as expected.
all .mp3, and my output settings are WASAPI and as far as I know are as vanilla as possible (i.e. I haven't changed them since installing MB)
The only program used to edit anything on the affected files is MB.
Thanks