Vsphere-iso upload to packer_cache hangs

I have a packer build which works in with an established vsphere I have in another environment.

But on a new vsphere (with the basic things like dns available) the upload of files fails.
I am able to upload to the datastore through the vsphere webclient just fine using the same account.

Packer authenticates fine, and is using an admin account so permissions are not a problem.
It created the packer_cache folder in the datastore okay, but just stalls in the upload without erroring out. It just gets stuck.

I manually added the iso, but the cd_files upload still fails.
Just hangs at this point:
==> vsphere-iso: Uploading packer1719812387.iso to packer_cache/packer1719812387.iso

Not sure where to even check.