Teamviewer on headless Raspberry Pi can only connect if user is logged in
I have installed Teamviewer 15 on a headless Raspberry Pi 3 withou Linux Mate (although I initially had a monitor connected because I needed it to configure SSH). Problem is that the Teamviewer host on the Pi is running and also appears to be online but when I try to connect to it, my Teamviewer hangs on "Connecting..." and times out after 3 minutes. If I connect monitor and keyboard to the Pi and log in, i.e. start a graphical session, the Teamviewer connection can be successfully established. What could be the problem?
Below is a log that shows the boot process and a failed connection attempt that ends in the above mentioned timeout.
[The logfile has been removed as per the community guidelines.]