Thanks so much @Mth for your great answer!
The second reason you listed was my case here, and after changing CreateDisplay to 0 (it was 1 indeed) problem solved.
BTW yesterday I found another way (a dirty one) to start desktop as user.
In node.cfg I just specified a bare graphic terminal xterm:
which started by player as root.
Inside xterm terminal I typed the command :
# xhost + username
which basically means ‘allow username to use display owned by root as if it was his own’
then switched to username :
# su – username
then started LXDE desktop as that user:
Can’t guarantee security of this trick but it worked for me. Only issue with it was no audio. Anyway this is of course unnecessary now after your solution, just leaving it here for general knowledge.
Thanks again 😉