My organisation has identified a number of bugs related to ready to use validation rules. We have experienced similar issues to what has been described above. There is a (vaguely described) bug here:
https://support.esri.com/en/bugs/nimbus/QlVHLTAwMDE0Mzc5Mw==
Esri Support's advice has been to not use ready to use rules, but create a standard validation rule and use Arcade to define the expression. 😞