Two more hosts? What I would do is
1. Check the hosts logs - both VMware and BIOS/system to help isolate a hardware issue
2. Loop in the hardware vendor - for unless someone has been locally trying to play around with the file systems, could be a case of controller caches/batteries/firmware etc having an issue - especially if all hosts that were affected show symptoms of having been rebooted as well
Below are some if the advisories that are in the public domain but I am sure each vendor would be having internal documentation as well if a particular hardware is affected
Regards
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