Type 0 and Type 1 midi files...need help

I made the mistake of freezing my midi track and now nothing happens when I try to play the midi track from a sound perspective. This happens not only in n, but also other midi editors. The events are there; they show up in the piano roll but there is no sound. What is going on here and does anybody know how to fix this? Using an older version, and don’t want to upgrade for this reason only.

version 7.1.2 build 3278

I should clarify. I clicked ‘Lock part offset & size’ and then exported the midi file and now nothing works.