In my continuing search for this problem I installed alacritty, which also shows a weird fenomena related to this issue:
% echo $TERM
xterm-256color
After restarting the emacs server and opening a file with emacsclient -nw I have to wait for 2 seconds for emacs to 'focus' after whic h the bar at the bottom changes to focussed and I can begin typing. If I type for example the downkey I get OB added at the cursor.