Card Expiration Integer Error

Have had a couple customers this past week call in saying the cart is throwing a Credit card expiration integer error. They have confirmed that they are only including numbers in the field, but cannot get the order to submit. Seems to be happening on ipad/iphone only, but we cannot replicate the error. This is on v 4.2.4

Has anyone else gotten this error?

Unrelated, but on our v3.0.6 site we have been getting similar errors, but they have to do with other fields. One was "incorrect zip code format" and invalid email error. Both seem to be on mac products.

Can you please explain what an "integer error" is?