In my cluster with 3 peers I brought down an availability zone at 10:05 containing the shc_captain.
The other two members were working fine.
At around 10:30 a new captain was elected and my old captain was downgraded.
If I bring down the single captain, a new captain is elected within 2 minutes.
What could be a reason for my cluster taking so long before an old captain is downgraded?
How long was the captain down? If you were running on two clustered search heads only for any period of time it is possible that the cluster encountered a split-brain situation. With only two nodes, a quorum can't be reached so neither is able to (quickly) decide/vote on who should be captain.