CiviCRM Log shows error invoking Payment Form
It looks like it's getting an error when loading the payment-processor specific part of a contribution form, via AJAX. It should be getting the payment processor id as part of the ajax call, but it's not. That suggests it might be on an old contribution page that had a payment processor configured as an option that is no longer available.

If you can look at your web server access logs and find the corresponding contribution page you might identify the problem. It's even possible that you wouldn't actually see an error on your form, it would only show up in your console.