Queue Failover destination becomes first destination when triggered

We have an odd problem with our queue failover behaviour. We have four static agents in our queue, which has a failover destination to a ring group. Sometimes, the behaviour seems to change, in that after entering the queue, calls go straight to the failover destination. The only way we can get it back to normal is by performing a reload.

It seems that the glitch may be triggered when a call legitimately goes to the failover destination. It’s as though this initial call is taking the static agents out of the queue.

Any advice on what may be causing such behaviour would be appreciated.