Hello,
thanks for the fast Response :)

we are running the Altis Life 3.1.3 "mod" but other @XXX Mods we arent running

just to "enclose" the Problem i've cleared all, and putted our "MP Mission" and "@live_server" files in the fresh updated Arma 3, also rechecked and updated the port forwarding for the new Update (2303).

i'll test it now for a few hours and let you know if it Comes back :)

edit: okay now one Player got the Session lost but the others can Play without Problems and get the Session Lost problem in a few minutes or hours later(thats strange :()