What do you see in the Tag column as mentioned in the same topic:
An early indication of such a problem is when Mp3tag doesn’t report any details about bitrate, length, … in the respective columns in the file list.
Starting with Mp3tag v3.12a, it also reports some of the issues found to the Tag column in the file list. Please make sure you check those.
Please also check "How to repair files identified as corrupted?"