If a spell that’s altered by Subtle Spell has no material component, then it’s impossible for anyone to perceive the spell being cast. So, since you can’t see the casting, counterspell is of no use.
and his ramblings
If a spell that’s altered by Subtle Spell has no material component, then it’s impossible for anyone to perceive the spell being cast. So, since you can’t see the casting, counterspell is of no use.