Macvlan call traces are usually the result of having dockers with a custom IP address, more info below.
https://forums.unraid.net/topic/70529-650-call-traces-when-assigning-ip-address-to-docker-containers/
So are most SATA disks, still too hot, you should keep them under 40C, 45C tops.
Power on hours can't be changed, unless there's some firmware issue they are correct.
Do you mean new to you? Disk is very far from new, it's also running very hot.
Diags are after rebooting so we can't see the error but wait for the result of the long test, though I would strongly recommend to improve cooling.
See turbo write for better write speeds, but note that having two users writing at the same time will still slow down Unraid a lot, Unraid doesn't stripe disks, so it can never perform as well as RAID soltutions, it does have other advantages though.
du isn't reliable with btrfs, space used on the GUI is correct, note that if you have for example a vdisk on cache the file can bloat way beyond the reported used space, this can help with that.
This now suggests a device limit, after the RAM cache is exhausted, enable turbo write, write directly to one of the disks and grab the diags after it slows down, then post them here.
Disk2 only shows filesystem corruption, not ATA errors, that should be fixable by checking filesystem:
https://wiki.unraid.net/Check_Disk_Filesystems#Checking_and_fixing_drives_in_the_webGui
If the new cables didn't help it almost certainly a disk problem, sometimes errors are weird, just recently had a disk that passes every SMART test, you can do a perfect copy with dd, but try to mount the disk with any filesystem and you get error after error.