When a networked A gate, with a valid destination, is active, it's iris will be opened to the relevant traversable material.

This is intended; users entering the gate in question will exit at the applicable destination.

When the server restarts however, there is a visual problem; the IRIS does not close despite the gate being inactive.

Users or entities attempting to enter the gate will be unable to use the IRIS material.
For nether_portal, this means infinite nausea with no teleportation, no nether, and no error messages.

Thus, from a UE perspective, may be best to deactivate IRIS materials from A gates on shutdown.

Note that this problem may also be related.