I have several remote systems setup for unattended access. My work system will show as online for days or weeks, and then it goes offline. But when I check on it in person, the client is fine. Rebooting doesn't get it back online, etc. I have to open the computer and Contacts on the sytem and under "Offline" I delete the system and then I click on Add This Computer. Or what ever it is called. It then gets re-added and it back online again. And it will stay that way for days or sometimes weeks at a time. And then it goes offline again. The system does not go to sleep and if fully on when I come back to the office. Driving me nuts and this is the only system that does this.
It's a Windows 8.1 system, but so are many of my systems. And trying to search for teamviewer offline gets me different offline issues.