Field stopped appearing in latest version?

Olá Marco!
For our store we use CheckoutWC which replaces the default woocommerce checkout.
For some reason all versions up to 4.6 of the NIF plugin have worked well and the field shows up normally, however we recently updated to the latest version of the NIF plugin 5.1 and the field now doesn’t show up anymore.

If we disable CheckoutWC everything works normally again, but if we rollback to 4.6 then it all works together fine.
Could this new change of the woocommerce_nif_field_validate?filter somehow have affected/changed something on this end??
I couldn’t find if there is some input to turn this validation on or off.

I have also already contacted the CheckoutWC developers about this issue.