Archaludon evolved from a Duraludon caught in Galar is flagged as invalid. This also marks Galar ribbons, HOME transfer moves, and OT memories as invalid.
Also shiny female 1/8 Pokemon transferred from gen 1 VC should not be flagged as illegal because there was a small window of time between when Poke Transfer worked with RGBY and when GSC released where gender was calculated randomly and shininess was calculated incorrectly. This means that shiny female VC Bulbasaur, Eevee, etc. should all be considered legal. This issue has been around for a while though, so I don't expect that you'll change it, but it would be nice if you did