Advanced application restart gated by Delete lock
At the moment, if there is a Delete lock applied to an App Service, it prevents the Advanced application restart feature from working. Reference ticket 119060721001994.
It appears that Advanced application restart is an older feature implemented before locks were exposed, and it issues a DELETE HTTP request to perform the Advanced application restart, which is denied due to the Delete lock being in place for the app service.
This is inconsistent with other actions that effectively do the same thing - via Restart, Scale Out/In, Scale Up/Down, and Kudu process kills. Note that Kudu is the only way to target a particular instance to restart when a Delete lock is in effect.
The workaround is to remove the Delete lock, issue the Advanced application restart, then reinstate the Delete lock. This is not only clumsy but prone to error given that the Delete lock has to be removed - defeating the purpose of the Delete lock.