Unfortunately doesn’t seem to have worked. I pulled an un-updated (1.20) copy of the plugin Content from a different engine version yesterday and everything popped back into place, after today’s update same problem as the original 1.21 update.
Repeated on UE 4.26 and 4.27, roll-back to ProInstance 1.20 fixed everything.
When transforming ProInstances they would expand out like with multiple objects, but then snap back to where the variables are set, appears that’s missing now and the distance between is being multiplied with the scale. An X distance of ~400 on a ProInstnace Grid scaled to ~1.87 had the measured distance in game world increase to ~748 after update.
Currently 1887 ProInstances in my other world (1254 in another, 981 in another), thankfully if you have the 1.20 content it all goes right back to place.