Cannot queue stack: stack exceeds maximum depth

[jeenkhoorn]

Hi, a few of our PRs fail to queue with the error "Cannot queue stack: stack exceeds maximum depth. Stack exceeds maximum depth of 20."
The merge queue is empty and there's no sign of outage on https://status.mergify.com/
What could be the cause for this issue?

[jeenkhoorn]

FYI the issue is tracked here: https://statuspage.incident.io/mergify/incidents/01KMQEQ9YEVC1K9JHB83W2ZGE5