Hi,
I don't have ONTAP 9.7 in production so can't really verify for you but in VMWare ESXi/vSphere you can mark a "disk" or "LUN" as "FlASH", indicating that the disk is an SSD (SSD/flash storage backed). However, as I am reading about it more, it says that if you mark Spinning Disk as 'Flash' it can seriously deteriorate datastore performance, so you have to be cautious.
Has anyone (In your team) marked them as 'flash' accidentally ?
https://docs.vmware.com/en/VMware-vSphere/6.0/com.vmware.vsphere.storage.doc/GUID-99BB81AC-5342-45E5-BF67-8D43647FAD31.html
While you confirm the ESXi settings from your side, could you give this output:
Please enter the name of the aggregate below that is hosting the 'LUN' on your FAS Box.
::> aggr show -aggregate <aggr_name> -fields storage-type
Also,
::> version
::> system show
Thanks!