The log says the hosts are "temporarily disabled" when the interface is detected as down, however the items are still listed in the queue. It is occurring for JMX and Agent items.

Upgraded this instance and its proxies to 2.2.2 on March 17th. You can see in the queue graph that after the upgrade, the queue is staying much higher.
This bug seems to be affecting all versions of 2.2.X.

(The frontends are now running 2.2.1 because of another issue we're having when importing templates.)