Round robin not processing backlog tickets

We set up a round-robin for one of our departments which initially worked, but something seems to have broken during the 'tweaking' process as it will no longer assign backlogged tickets of any kind. (I've included images of the settings.)

Based on the round robin's "Incoming Tickets should be" setting, we would expect either:

"Assigned to agents"
Agents are online: ticket is auto-assigned immediately

Agents are offline: ticket is added to backlog-queue; queued tix are auto-assigned as agents come online

OR
"Added to backlog"

Agents are online: ticket is added to backlog-queue; queued tix are auto-assigned as slots become available

Agents are offline: ticket is added to backlog-queue; queued tix are auto-assigned as agents come online

But what happens is:

"Assigned to agents"
Agents are online: ticket is auto-assigned immediately

Agents are offline: ticket is added to backlog-queue and remains there until manually changed

"Added to backlog"

Agents are online: ticket is added to backlog-queue and remains there until manually changed

Agents are offline: ticket is added to backlog-queue and remains there until manually changed

I've tried adjusting the "Assign Backlogs" options but nothing seems to help. Any assistance is appreciated.