I tried several times with the same version of gimp from the stable channel(2.8.22 (25)) on my laptop. It works fine even though some warnings and error messages popup at startup.
$ snap version snap 2.28.1 snapd 2.28.1 series 16 ubuntu 16.04 kernel 4.4.0-96-generic $ /snap/bin/gimp Gtk-Message: Failed to load module “overlay-scrollbar” Gtk-Message: Failed to load module “gail” Gtk-Message: Failed to load module “atk-bridge” Gtk-Message: Failed to load module “canberra-gtk-module”
But looks like you’re not the first person to hit this problem. It’s bit weird.