Hello.  I have been using TEAMVIEWER to run a small support desk and have a corporate license.  I have version 15.5.3.  For  the few years i have been using it, it is great.  
I am noticing a stream of clients on my COMPUTERS/ CONTACTS that are Online, but unable to connect.  There will be no error message, just 'connecting' when attempting to connect.  After about 5 mins, it will go back to ready to connect. Reboot has no impact to the remote connection. 
If it is just one client, i would of just thought it was that one unit that is just messed up.  Right now, i have confirmed over 50 units on my list that have this symptom. I have confirmed that port 80/443/ 5938 are opened. I have loaded other remote software on the local units and can confirm the system is alive and running.  Just not TeamViewer.  Any assistance?