I recently ran into a weird issue trying to send service alerts and I suspect it's a bug in the backend.

I had configured a few of our services with the service tags: alert=observability-availabiltiy

and then had also created service actions with the matcher critera to match where tag name=alert and value must contain observability-availability.

With that configured I could not get zabbix to send me a single email, so I tried playing with the service tag value first, then I started to try different names.  As soon as I tried any different name it works as expected, I can even use the name alerts, but not alert.  As soon as the tag name is alert is does not seem to want to send an alert for some reason, you can't find it in the audit log either.

Anyways, just thought I'd post my finding here.