Why is the Optmizer suggesting hit gems for a Disc priest?

TIA for the help – I do have it set to “Healer” and I am in my Disc spec.

I need a snapshot of your case to look at this further.

The most likely reason is that you have shadow set higher in the spec priority list on the left (not in your screenshot), so the gear is being gemmed for shadow and then the optimizer can’t change it for discipline.