One of my players is using a Forest Gnome illusionist which comes with Minor Illusion (Natural Illusionist) as a race feature.
Once the character levels up to 2nd level, they are given the option to join the school of illusion which is supposed to give them Minor Illusion, but if they already know the spell then the option to pick a different cantrip.

The system is not allowing them to pick another Cantrip.
The spell is not showing as a learned spell in the manage spells section so we cant "Unlearn" it.

I have gone into their sheet from my side and the spell shows in both the Prepared Spells and the Spell Book.
I tried to delete one of the spells but it errored and now the spell isn't showing in the Character Builder: Class section.
Its acting as though the spells didn't recognize they are same and glitched.

Is there a fix for this or does a Dev need to look at this? 

Thank you.

This is a known issue. The general systems/backend updates that they're working on will hopefully fix this, but we as users have no info on when that might happen. In the meantime, the suggested workaround is to grant them a free homebrew feat with the cantrip of their choice.