@earthendev : I took a look at your file and it has 137 bones - which is a lot! The “default rig with no toes”, I believe
So, I created a basic figure in MH1.1 to match it, then tried exporting it fro Blender (v5.4.0) and I get this in the log file:
Skeleton stats:
WARNING: Maximum # of influencers exceeded for 226 vertices, extras ignored
Total Influencers: 42480
Avg # of influencers per vertex: 4.3798
Highest # of influencers observed: 11, num vertices with this: 226
exported as 8 influencers
That maybe is your problem. You could delete the Pelvis.L and Pelvis.R bones - and see what you get.
Those 226 vertices mentioned could be the ones going adrift.
cheers, gryff 