Loops ignored in Mechanim

So this is weird.
I am adding two new anims to a project and dropped them into a blend tree. They play once in the preview but do not loop, instead the timeline ticks on and they are frozen. Same in the game.

Both clips have loop time on.
Both clips have the correct end frame set.
Both clips have the right rig type and avatar.
Both clips preview correctly in the fbx import settings.

No dice. They just refuse to loop in the blend tree.

Adding any other loop anim to the blend tree works, it seems to be just these two.

Same animator, same source file, same rig. Preview plays fine once, but only once.

I am going nuts here

 

The clip also works when dropped into mechanim normally, but once inside a blend tree... nup, not happy.

Any ideas at all at this stage, no matter how whacky?

 

I ended up deleting the meta files and voila. So corrupted metafiles?

 

A while ago I tried to make a menu function to toggle looping on a whole bunch of animations at once and encountered a potentially similar issue. The function ran fine and the Inspector showed the Loop Time toggle had changed on them all, but when I went to actually play the animations it just completely ignored the change and I never found anything to get it to accept the change other than completely closing and re-opening Unity.