Fillable form junk characters

Hello, I hope someone can assist with this as we were not able to solve the issue with possible solutions found on the forum or other support sites.

We have a fillable form that displays normally when the original empty form is first opened, like in the example below:

However, the moment you click on the Card Number field to start typing, the form characters break and it looks like this:

We have tried disabling the option ''Use local fonts'', we tried re-creating the form with different fonts or field types and it breaks every time. We tested in Adobe Standard 2017 and 2020 and the issue is the same.

Any ideas what might be breaking the form?

Thank you!