Quick Update:
So after a lot of tests and starting the project all over again I've now realized that this issue still persists in other projects, but only affects audio files that are made up of regions last of which starts at an "uneven" position.
For example, if the section that I'm trying to export is made of 2 regions and the second one starts "on the beat", let's say, at 75 2 1 1 (or 77 3 4 1; 123 2 2 1) then the resulting loop would be perfect. But if the last audio region starts at, let's say, 75 2 3 118, or 123 4 4 53 (so not on a beat) then the resulting loop is different in length than the original!
Any idea why this might happen?
I've obviously tried to move all of the affected audio so that the last region lines up with the grid but for some reason, it doesn't work. Looks almost like it remembers how those bits of audio were initially and it refuses to change its mind! And I cannot really play much with the content of the audio.
Any advice?