Hi,

are they a local datastores or shared over network like NFS?

If they are from network I will suggest you to check the whole network if its OK and you can access the shared storages.

If it's local I will suggest you to come to the shell and first check the stores if they are OK and do you see it. 

Then You should try to unmount it and then again to mount.

And I have also fount this to your problem what you should also check:

 - This issue occurs if there is a mismatch between the Jumbo frame size in the router and the vmkernel MTU settings.

- https://kb.vmware.com/s/article/65169

Hope it helps.