Removed a disk from a mirrored pool, with a spare attached. Upon removal, pool showed degraded, and spare was activated and put in use by the system (690 screenshot). UI shows pool degraded on dashboard and under Storage/Status (screenshot 363).
Once drive is placed back into the system, pool status does not change to online (screenshots 389/244/112/311). Also, pool cannot be disconnected/exported in this state. Workaround for this is restarting the system. Once up, pool shows online and pool can be deleted.
This was checked in several different browsers, with all the same outcome (Edge, Chrome, FF).