Can’t speak specifically for the wiring of the Strymon 3 button, but the h90 should work fine with a normally open switches connecting:
tip to sleeve
ring to sleeve
tip and ring to sleeve
assuming the Strymon does this, I would confirm you’ve correctly configured the exp port as a 3 button switch and not an expression pedal per:
https://cdn.eventideaudio.com/manuals/h90/1.12.5/content/system-menu/io.html
