I would say this is the most weird issue I ever faced, it took me so long to find a solution so thought of making a note of it.
My setup is all nested, VMware workstation on my Lab Windows PC and then ESXi, vCenter and everything else as VMs running on workstation.
After building a vSphere 6.5 lab environment, when I deployed my first VM and tried to power it on it got stuck at a some point, after waiting for few minutes when checked the task and events, found following info event there,
"Running VMware ESX in a virtual machine will result in degraded performance. Do you want to continue"
Then I created few other VMs but they all got stuck at some random point during power-on operation and the same event was there in events.
However there is no way to answer the question, nothing in VM summary and no pop-up nothing.
A quick search about the issue lead me to VMwareb# 2108739 however adding msg.autoAnswer = "FALSE" in host .vmx file or /etc/vmware/config didn't make any difference.
Initially I thought this is something related to ESXi 6.5 so, just to check deployed another VM with ESXi 6.0 but even on nested ESXi 6.0, VM power-on operation stuck at random point.
Earlier, I had a working vSphere 5.5 nested lab on this system so, thought of checking with ESXi 5.5 but to my surprise VM power-on operation got stuck with same "Running VMware ESX in a virtual machine will result in degraded performance. Do you want to continue" question (without any way to answer it) for ESXi 5.5 too.
Then I thought this is something related to VMware workstation so, downgraded it from version 14 Pro to 12 Pro but there was no difference.
This is when I started looking at other things and eventually found that its my antivirus which was causing this issue.....Avast Antivirus...... enabling or disabling the features in the software did nothing however uninstalling Avast worked like a charm and now everything working again as expected.
Hope this would help...
That's it ...:)