MASH blend deformer results in flashing waitCursor in 2020.3

[mcw0]

I applied a noise texture to a MASH blend deformer on one mesh.  And the waitCursor starts flashing on and off.  And the file became practically unusable.  Anyone else encounter this and found a workaround?

[mcw0]

I redid my rig starting with the MASH blend deformer first and everything is ok.  The profiler didn't report any issues.  When playing back, it was slow but ok.  But interactively, it was useless.  If anyone has an explanation, I'd love to know what it was.