I more recently noticed this problem, perhaps over the past several weeks. I have my home theater PC, running Windows 10, connected via TeamViewer. When it first boots, it will sit at a Windows login screen. I have set up TeamViewer for unattended access, so I do see it on my list of available computers.
However, after a short period of time, OR if the computer was unlocked but then reverts to a lock screen, I will lose the ability to access Teamviewer again. I am quite certain it was not always like this.
Yes, looks like the same problem. Using any method (PC app or phone app) shows the same result.
Are you running Windows 10? Maybe one of the infinite updates pushed out changed the behavior of the Teamviewer service?