F
Flintstone
None of the gritty none porous surface primers form a skin of any sort. No matter how you apply it, from my experience, but as said above. Bostik isn’t a reputable brand to professionals!
Yes, you can scratch off, but not peel off. The force of tile adhesive and tile onto the primer is not gonna pull it off
You could always call their tech line/cus service this morning and check with them.
Odd as it seems I suspect its as it should be.