We have a situation(reproducible) where a member belonging to both an "overnight" shift and a "daytime" shift in the same day will not get notified at night. instead, it will hold until the morning shift starts.
I found something similar described at this link: https://support.xmatters.com/hc/en-us/community/posts/210123186-Rest-API-Get-whos-on-duty-409-conflict
So, I followed the articles advice and "copied" the shift. Here is the message I was seeing. It is now gone.
But, the problem persists. Overnight messages to Dan Bergerman will not get delivered until 7:00am the following morning.