I recently grew a datastore (SANSF01) from 4.5 TB to 5TB in a 2 ESXi cluster. All worked successfully, However occasionally vCenter will show the old value and thus give us a warning about low disk space. a "Refresh Capacity" forces the value to be correct (5TB) but when I look back later on in the day it will be back down to 4.5 TB
I logged into ESXi host #1 via SSH and ran the df -h command to show what the hosts were reporting
As you can see the correct value of 5TB is showing. I then looked at ESXi host #2:
As you can see this host is showing the old 4.5TB. I went back to the vCenter and did a rescan on the host. I then went back to the CLI and ran the same command and the correct values showed up. In turn, this fixed the vCenter values.