I compressed a drive that had about 500 xi & iti files in them and now MANY of those files lost their loop points data in the samples and envelope data in the instruments!! what happened to those when I compressed the drive??
I really don't know (it shouldn't happen), but many years ago I do the same and I got a lot of corrupted data. Copy files to a uncompressed file system, and disable it on the one you have stuff. Personally I don't recommend file system compression because it's slow and you can't achieve good compression ratios. It's best if you use an archiver like 7zip, which has a very high compression ratio. Also you may create a dedicated partition or get another drive to store your data.
And why exactly should that be an issue with OpenMPT? File system compression is completely transparent to programs, so as jmkz suggests, your files might be corrupt and there is no way to restore them. The probability of such a corruption only affecting loop points and not the sample data itself is practically zero, though, so I'm just guessing that you are making up stuff again and the loop points were never there.