I've had these settings running for at least 2 years. When a person walks up my front walkway, the motion in blue iris triggers the built-in Code Project AI to determine if it is a person and if it is, sends a notification to my Hubitat hub to play a chime in the house. This has worked surprisingly reliably for all this time, at least 2 years.
2 days ago I noticed I wasn't getting SOME notification chimes, but then I go to test it and it works. I'm finally digging into this and it seems that randomly, for no reason that I can understand, blue iris motion is not triggering. My motion trigger settings should trigger almost everything (and then allow AI to filter); small object size, min contrast, .2 Make time....
And if I go back to these events where it's skipping marking the motion, and run a TEST motion, it shows as triggering the motion immediately.
This is very frustrating because I haven't changed any settings and the motion trips in playback/test mode. And it's not consistent. It's almost like the motion portion of BI goes to sleep randomly and just plain doesn't work sometimes.

A little more info that may be helpful:
I'm on the latest update. My CPU idles at 30% while its recording all streams. BI runs as a service with usually no display on. BI is installed on a dedicated PC with a GPU for AI, and the CPU is an i7 6900k

I would start with the basics. Set up the Log file to write to a text file; I have it writing to desktop as it only creates one file a month. Follow that by saving the interaction between BI5 and CPAI to get a DAT file. Between the two of them, this should tell you what is or isn't working.

At the risk of stating the obvious, did you look in "cancelled alerts"?