The recycle bin was empty. System Volume Information folder was empty
I think I may have found the problem.
On removing the Poolpart.27099acc-9b43-4aff-8854-db05102694da the HDD was still reporting 1.6TB used by Aomei partition assistant! I removed all the partitions on I: & created a new partition. I removed the I: drive from the drivepool & then re-added it to the pool. The phantom 1.56TB "other" on I: has gone!
I don't know what caused this problem but, for now, it's fixed
Thanks Shane for your input.
dominator99's post in 1.6TB 'other' on 1 of 8 HDD's in a 29.1TB pool was marked as the answer