The Office 365 Exchange Online Mailbox Rule editor isn't working correctly when trying to add a User Properties condition, e.g. "Sender has specific properties include any of these words" or "Sender has specific properties matching these text patterns". There's a UI glitch where the "Select User Properties" pop-up doesn't allow you to enter in words or patterns. Verified this problem in both the old and new Exchange admin centers.
Discovered in this 2015 thread that it only works in Internet Explorer, which is still the case today -- https://answers.microsoft.com/en-us/msoffice/forum/all/unable-to-add-a-property-rule-to-the-recipien.... A YouTube video from that post showing the problem https://www.youtube.com/watch?v=IT4jyWbBmYQ. I was able to add the rule using IE11, however the new admin Exchange center doesn't support IE11, so hopefully this problem will be fixed soon.