Hi Kerry,
I just tested your xlsx form in 3.10 Connect and field app and it is working as expected without making any changes. I am able to add multiple photos to the one image question, and when I add 4 photos (your constraint only allows 3 photos), when I try to submit the form I get a constraint validation message as expected.
I would suggest updating the constraint message to be more informative regarding the number of allowed photos.
Regards,
Phil.