As usual, you have to fix the type-unstable code in GMT. (That’s a lot easier now that Cthulhu is user-friendly.) Or, now (with PrecompileTools 1.1 and higher) you can create a personal GMTStartup package, and load both Revise & GMT under @recompile_invalidations.
But it looks like SnoopCompile has bugs due to some of the changes. There are clearly invalidations to GMT code that it’s not inserting into trees. Can you please file an issue at SnoopCompile?