This component is massive so I'd recommend refactoring it so it's a bit easier to read. (Is it also redundant to have two validations, one in the checkField() function and another written in RHF? You can test/validate only dirty/touched fields in RHF I think, they have examples of multi-page forms.

Anyway, an initial sniff, I think it's because of the watch - it triggers a re-render on every input change so I would remove that, if needed, use the useWatch hook.