Disk Removal Detected but all looks ok? ReadyNAS NV+ V2 running 5.1.13

Hi. Over the last few days I've tried to create a new Windows 7 VHD which took days, so I aborted it. In investigating why it was taking so long I discovered that the NAS network interface was only running at 100Mb/s, so after a lot of scrabbling around and substitution it turned out my switch has gone faulty, which I've replaced. Now I notice that the logs are telling me I've lost a disk (not having much fun here!!!).

Tue Nov 14 16:12:29 WET 2017:A disk was removed from the ReadyNAS. One or more RAID volumes are currently unprotected, and an additional disk failure or removal may result in data loss. Please add a replacement disk as soon as possible. 
Tue Nov 14 16:12:29 WET 2017:Disk removal detected. [Disk 1] 
Mon Nov 13 21:16:39 WET 2017:System is up. 
Mon Nov 13 21:09:10 WET 2017:If the failed disk is used in a RAID level 1, 5, or X-RAID volume, please note that volume is now unprotected, and an additional disk failure may render that volume dead. If this disk is a part of a RAID 10 volume,your volume is still protected if more than half of the disks alive. But another failure of disks been marked may render that volume dead. It is recommended that you replace the failed disk as soon as possible to maintain optimal protection of your volume. 
Mon Nov 13 21:09:10 WET 2017:Disk failure detected. 
Mon Nov 13 21:08:57 WET 2017:A disk was removed from the ReadyNAS. 
Mon Nov 13 21:08:57 WET 2017:Disk removal detected. [Disk 1] 
Mon Nov 13 21:03:12 WET 2017:UPS has been disconnected. 
Mon Nov 13 20:59:42 WET 2017:System is up. 
Mon Nov 13 06:25:35 WET 2017:Volume C is approaching capacity:

Disk 1 in the Info display looks a bit lacking in info compared to the other disks too:

Disk 1:0 (0 °C / 32 °F, Write-cache On). Status: OK
Disk 2:WDC WD30EFRX-68EUZN0 2794 GB (42 °C / 107 °F, Write-cache On). Status: OK 
Disk 3:TOSHIBA DT01ACA300 2794 GB (40 °C / 104 °F, Write-cache On). Status: OK

So on one hand I'm seeing "OK" relating to the disk, and the hardware blue led is lit, on the other the disk info is missing and the log says the disk has been removed. I was just going to yank out and replace disk 1, and let the system do it's job rebuilding the RAID, but I thought I'd ask if there's a better way to do it, or is there something more sinister to worry about.