I run a HP G7 N54L which has ESXi 6.5 installed, its getting old but its brilliant.
Anyhow, I ran a Windows 10 VM which I had Plex installed on, for some reason Plex gave up the ghost so I decided to install Ubuntu and was planning on installing Plex on there.
Grabbed the ISO and installed and 5 minutes after install the Ubuntu server froze, so rebooted, froze again.
After some digging I post a post that mentioned its a hardware issue sorted in ESXi 6.5 update 1.
So downloaded and update my server (note there was a warning that future releases of ESXi wont be supported on this CPU) and ran Ubuntu and it worked flawlessly.