A couple more thoughts...
Different woods/scales will expand/contract different amounts with humidity than others, so some scales are naturally less prone to shrinking than others, although all will do so to some extent. Also, woods expand/contract at different rates in different directions, so the orientation of the grain can make a difference also.
Mineral oil is a finish that never hardens in the wood. It is a good food-safe finish (great for cutting boards, for example) and easy to apply, but must be replenished regularly (especially if the wood is washed) and won't do as good of a job at sealing wood against expansion/contraction as other hardening finishes. It still helps though. And of course you'll never see it delaminating from the wood surface or chipping off.
I live in a climate where everything shrinks. Sometimes I will just sand the tang a bit to ease the feel of the shinking scale. I have never had one bounce back with mineral oil, but like Dave said, it can't hurt to try.
If it is pakkawood then it's just a laminate. Not sure how much a mineral oil will help/penetrate but you could try it. If you have access to a cryovac machine you could always try to vacuum the knife in the mineral oil on high pressure to try and force it in there a bit. I do this on regular wooden handles and sayas to great effect.
Starting this harvest I'm a starving startling artist/
Lyrical arsonist it's arduous spitting this smartest arsenic/
good idea! =D
The scales on my Hiro shrank and the tang was sharp so I replace them with Ironwood. I have the same problem on my Hankotsu so that will be getting new slabs soon.
I just noticed the "resin-stabilized" scales on my old Tojiro shrank significantly. Depending on your climate, it can happen to lots of things. It sounds like you now have a good excuse to rehandle!