Hi @simkessy ,
Just an update -- Currently, the issue has been fixed within Custom form in SP List.
Please consider clear cache of your browser, then try your custom form in your SP List again, check if the issue is solved.
If the issue still exists, please consider remove the custom form from your SP List, then re-create a new one for your SP List, then run your custom form again, check if the issue is solved.
If you have solved your problem, please go ahead to click "Accept as Solution" to identify this thread has been solved.