Same issue here. Had this problem since I bought the Key2. I did a lot of research concerning this issue. This seems to be related with google oreo (8.1) update and persists also with Pie update. Many Android users using a variety of phones (even the latest phones) are facing this huge problem.
https://support.google.com/pixelphon...d=1C0ZGY3nAQAJ
https://forums.androidcentral.com/an...d-stopped.html
https://forums.androidcentral.com/go...ter-8-1-a.html
A factory reset didn't help to solve the issue.
I have decided to go back to the keyone (to see if it's a key2 problem or not). I bought a new keyone to test out if this problem is there. When the keyone was on Nougat update (out of the box), notifications were running perfectly. After it updated to oreo OTA, the problem came back (no notification sounds - even thought all notifications are set to urgent and battery optimization is off).
I don't think it's only affecting a few phones as BB mobile said.
This should be fixed in a matter of urgency.
Google or blackberry should address a fix to this asap.