If you acknowledge alert using button, try to acknowledge it manually using instructions in your notification email.
If it will not help please bundle logs and attach it here.
What email client do you use?
I retrieved the logs this morning and believe I found the problem. I resolved the issue after seeing issues related to the email poller failing after trying to use POP. We use an Exchange system and nothing is setup for POP. I checked AC's settings and sure enough, the incoming email was setup to use POP. Changing this to EWS seems to have resolved the problem almost immediately.