gimp-gmic-plugin 1.6.9_1 is oudated very long time. Outside is version 2.4.0 and also version for GIMP 2.10 which is in the ports now. The old version doesn't work with new GIMP.
Fix bug title and fix auto-assign fail.
BTW, graphics/gimp is still at 2.10.8 in the freebsd repo. Shall I open a ticket ?