I was asking myself why a filter rule didn’t work and I had a RAW filter that had as action to 'return" and in Filter Rules the main rule did not trigger.
When I looked in the rule itself I found a open field without any content in it and that made the rule not being triggered. The field is the lower part and the label is “Connection Type”.
It would be great if on ‘apply’ winbox check gives a warning, or if a field is empty it will make the field inactive on applying.