Welcome to the Community,
I assume that you are talking about the automatically created VMFS partition on the installation disk!?
Can you confirm that both hosts were installed (fresh installation, i.e. no upgrade/reinstall) using the same ESXi version/build. At least the first ESXi 6.5 builds still formatted the VMFS partition as VMFS5.
Correct, I have installed on both servers a fresh ESXi 6.5 update2 version and I am referring to the default datastore1 created with the installation disk.