RDP failure and resolution

Last week, I could not remote desktop into one of our servers which was a VM on Azure - Remote Desktop was working only immediately after a restart, and later not at all. Remmina failed with

connected to ip.address.tld:3389
recv: Connection reset by peer
Error: protocol security negotiation or connection failure

and rdesktop failed with

ERROR: CredSSP: Initialize failed, do you have correct kerberos tgt initialized ?
Failed to connect, CredSSP required by server.

I thought I got the explanation for CredSSP from this post and thought disabling NLA would solve the issue. But then, I could not connect at all. I'd done this by right-clicking on System, Properties, Remote, and disabling the check-box 'Allow connections only from computers with NLA...' 

Tried resetting the connection configuration from Azure portal, still no. (Choose the VM in Azure Portal, Support + Troubleshooting, Reset Password screen, choose 'Reset configuration only').

I tried logging on using a Windows 10 VM on another server, but got an "internal error". Perhaps this was due to the Windows trial license expiring on that machine. Today when I re-installed a trial version of Windows 10 and tried to connect, the Remote Desktop connection worked fine. Turned on NLA, it still worked. Tried with Remmina on my local machine, that also worked. 

So, why did it fail and why did it start working again? Was it due to a Windows update causing issues like in this forum thread? Perhaps a network glitch? Perhaps restarting the VM (which I did several times) or resetting the configuration solved the issue but I was unable to check due to turning off NLA? At that time, I did not see this post, but maybe in the future I might need these tips again.