FWIW I normally use Pro Sports Contour Power grips in 25/32" & 3/4". I have tried and like Vise-Grips inserts, but, for me, they run slightly larger. So when using Vise, I use their half size, 49/64" & 47/64" inserts.
As itsallaboutme says, it could also be your fingers changing for any number of reasons. For me, a little arthritis and a little too much writing and my middle finger has changed slightly. I need to either open up the 31/32" drilled hole with sandpaper before gluing in the inserts OR I need to open up the insert with a little acetone.
At one point, my driller was using a worn, needs-to-be-sharpened 31/32" drill bit on the middle finger hole, because it drilled a hole just a tiny bit larger than a good sharpened 31/32" drill bit.
So, if your driller is using either a new or a recently sharpened drill bit, the 31/32" hole can be a little smaller than you had been used to.