Escalation policies suudenly require user assigned to On-Call Schedules?

[Marcin Stanczyk]

Recently we faced an issue when all of our alerts stopped being sent to our OEC instances for further processing. 

After some investigation we noticed that data is being sent to OEC instances if we change Edge Connector settings to work on "alert is created" instead of "alert is escalated" - so the issue was related to escalation.
We reached OpsGenie's support and after more investigating we discovered that the escalation policies work if they are setup to "Notify user" - in that case we need to provide a receipient.
At the same time OpsGenie Support told us that escalation policies based on On-Call Schedules only require On-Call Schedules to be enabled and there's no need for a user to be assigned to the schedule itself. Our case says differently.

The workaround for now which we implemented is to assign one of the users to On-Call Schedules for every Team, but this person cannot have any Contact Methods, otherwise he/she will recieve a phonecall/email to acknowledge for every alert that we want to send to OEC instances.

Also what's interesting is the fact that until 15.03.2023 escalation worked as intended, even though we hadn't had any user assigned to any On-Call Schedule. And then suddenly it stopped working.