tmux only possible as root and not as normal user in 7.3?

Hi there,

I have three new installed machines, that show the same strange behaviour: tmux is only startable as root, if I want to start it with command "tmux" as normal user (which is in wheel group, btw), I get the error "no sessions", if I try to start it with command "tmux start-server", the error is "no server running on /tmp/tmux-1000/default".
On another machine, where OpenBSD has been installed and upgraded since version 6.7, tmux starts without problems as said user.
I searched FAQ, manpages, www up and down and can not figure out, what goes wrong.
Is there anything I missed in manual or release notes? Was there any change in tmux startup?
Any hints would be highly appreciated!

thanks in advance
sarag