When I wanted to install CU11 for Exchange 2016, at the Prerequisites Check, I got the following error message:
"There is a pending reboot from a previous installation of a Windows Server role or feature."
I restarted the server twice, but still got the same message. After messing around with some registry keys and still no luck, I looked at the error message in more detail. The key part is "installation of a Windows Server role or feature". So this was not talking about a normal pending reboot because of a software installation, it talks about Server roles and features.
So I started Server Manager and installed a simple feature ("Telnet Client"). After that, the Exchange 2016 CU11 installation went through without problem.