How big are pull ratios in Shimano 9-speed front derailleurs in MTB and road bikes?
I've had something like this on two road bikes - the big-front and small-rear combo means the chain is running as far to the right as possible as it hits the front derailleur.

One was fixed by using proper-sized 9 speed chain, not the mystery chain that was already installed.

Since the limit screw is not the problem, you may need to shim the derailleur so the whole thing stands to the right a tiny bit more.  If its a braze-on mount this won't help.

Do test if you can move the cage far enough with your fingers (be careful!)

Another possible fix might be to distort the front mech's cage, but that may cause problems with other gears.