Another small issue, after approving a new user's first post and getting back to unread/all activity feed it still appears as unread, need to click on it again to be marked as read, this didn't happen before, it was marked as read after approving.
If you're up and running you can just reconfigure the LAN as needed, gigabit NIC should be eth0, and 10GbE configured using a different subnet and with just the IP address.
One thing would should do is to update the 16 port LSI firmware, might not be the problem but all p20 releases except the latest one (20.00.07.00) have known issues, if that doesn't help swap cables/slot with another disk.
You can do the update using Unraid.
Jan 15 11:55:48 Tower root: umount: /mnt/cache: target is busy.
Something still using cache, as for the unmountable disk no valid filesystem is being detected, you're sure it was formatted?
Both "old" disks look fine, disk3 is practically new, you can just do a new config with both and the rest of the array and re-sync parity, obviously will lose any data on those disks written after they were replaced.