“Null” and “undefined” on fields and submit button

Hi there, maybe someone else had this issue before? Adding new fields to a form, I always get a “null” above each field, no matter what field it is i.e name, checkbox or whatever. Above the submit botton there is “undefined” written! I already deactivated all plugins, but no change.

Thank you very much for any input on this

PS: The theme is “thegem” where I already used ninja forms in the past on another website without any problem.

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