Same issue was reported by our users from this morning.
One of the forms that had this error saved after removing the lookup dependent fields, i.e. those linked to the lookup field that only displays another related field.
Dear @Rinu, @Andre, @nI3o,
Thank you for reporting the issue! We've released a fix for the occasionally empty lookup field on Monday, but it has negatively impacted some forms, so we've also released a hot fix for that as well.
If you do notice any other issues - please, let us know, we'll make sure everything is working properly.