Hey, figured I'd send you a little update on the problem I had with the animations a while back.
Since then the issue did actually occour again and better yet, I found out why.
It did not have to do with the bone roll as I first suspected but with accidentally renaming a bone whilst animating. This ends up leaving an extra animation track on the timeline for that perticular bone and ends up messing with the animation. In blender this is hard to spot because the animation usually runs normally after this but when the animated model has been imported to game maker it only runs the new messed up timeline for that bone. I noticed this in blender when I switched between diffrent actions in blender because the animations would get messed up there too when I did so.
This is a really weird problem that is a tad hard to spot but it's actually quite easily fixed by renaming the bone back to it's original name and deleting the unwanted new timeline.
Not sure if there is anything you can do with your extension about this but I figured I'd bring it up in case you get other people with the same issue contacting you in the future ^^