We have three different clients reporting erratic errors on public-facing and administrative credit card donation forms.
The error is that CiviCRM reports that a credit card + expiry is invalid, and the error shows up before talking to the payment processor, i.e. it's form error, not a payment processor error. We've confirmed that the cc credentials are in fact valid.
These started happening after the latest (Nov 20 2019) security update (some on the 5.13.7, some on 5.19.2, not all using the same payment processor).
See attached picture for a clue: note the title of the cc images.