Phantom disks reported as not healthy?

[enCrypt]

Hello,
Not sure if this is in the right section...please move if not...

I've been playing with TrueNAS Core 12.0-U7 recently for the first time.
I have a RAIDz1 Pool that I setup using some old disks just to try it out.
I've had to replace all of them as they were faulty.
I've done this one at a time, letting it resilver etc...

However, now I keep getting the following alerts...some for disks I've swapped out, so they are not even in the system anymore...

CRITICAL
Pool Pool1 state is DEGRADED: One or more devices has experienced an error resulting in data corruption. Applications may be affected.
The following devices are not healthy:
Disk HGST HUS724040ALA640 PN2331PAJT6TTT is DEGRADED
Disk ST3000DM001-9YN166 Z1F1954G is DEGRADED
Disk TOSHIBA DT01ACA300 94PK7K6GS is DEGRADED

Those bottom two are ones I've swapped out so why would the system report them as not healthy?
Do I need to do something to clear out the references to the old disks?

Also, I upgraded the 3 x 3TB to 3 x 4TB disks but have not seen any increase in the size of the pool either...
I understood this would just happen automatically?

Thanks
enCrypt