I have this happen also, even after 2 surgeries. Yes it happens more under stress. I think it may be the muscles, not so sure tho. Let us know if u find anything out?! Maybe its instability, tho my ns says I don't have that. He also told me I didn't have eds, but my rheumatologist dxs me with it. Hmmmmm
It does happend to me sometime. It usualy when I'm tired or extermly stressed!