According to previous diags you assigned old disk1 to parity slot, and that's a shame since you had the diags posted here, so just needed to check that if you weren't sure which disk was which, and since the parity sync run for a few minutes that disk will now also be unmountable.
You can force rebuilding that disk using the invalid slot command but note that since the array was started read/write parity won't be 100% valid, there may be at least some fs corruption, follow the instructions bellow carefully and ask if there's any doubt.
-Tools -> New Config -> Retain current configuration: All -> Apply
-Check all assignments and assign any missing disk(s) if needed, assign old parity as parity, and current parity as disk2 (or 1 if you want, data disks order doesn't matter with single parity)
-Important - After checking the assignments leave the browser on that page, the "Main" page.
-Open an SSH session/use the console and type (don't copy/paste directly from the forum, as sometimes it can insert extra characters):
mdcmd set invalidslot 2 29
(assuming you assigned that disk as disk2, if it's now disk1 replace 2 with 1)
-Back on the GUI and without refreshing the page, just start the array, do not check the "parity is already valid" box (GUI will still show that data on parity disk(s) will be overwritten, this is normal as it doesn't account for the invalid slot command, but they won't be as long as the procedure was correctly done), disk2 will start rebuilding, disk should mount immediately (possibly not in this case) but if it's unmountable don't format, wait for the rebuild to finish (or cancel it) and then run a filesystem check.