Today I found out that the issue may be related to GNOME only, because the GIMP in sway works normally but the problem persists when in GNOME.
GNOME version 3.32.2
$ gimp --version
GNU Image Manipulation Program version 2.10.14
$ guix describe
Generation 57 Feb 26 2020 12:28:15 (current)
guix b68f5a6
repository URL: https://git.savannah.gnu.org/git/guix.git
branch: master
commit: b68f5a68f895307ee184da725882d6f243ccded6
