Thank you very much for the reply!
After initially searching the forums for my problem I came across
this thread,
where you explained some of the quirks with GameMakers Spine integration.
So I immediately made sure to set keyframes for all those properties at the start and end of my animations;
sadly this didn't solve the issue for me.
You did give me an idea though when you mentioned 'every' bone.
Could it be because the character only has one bone, and GameMaker needs at least two?
- Jeremy