MPT isn't something you should make XMs with... FT2/MT XMs work mostly fine.
If using MPT, you must use "Compatibility export" for all non-MPTM/non-IT modules.
Libsndfile isn't used for playback, that's just Onu's dependency. Onu itself uses D.U.M.B library. Most of problems are coming from it, this library wasn't updated for 13 years after all...
I'll see if i can switch the library. I'm also planning to rewrite this program later, cuz current version isn't really supposed to be released. I was requested to publish it