it seems like it is related to the validation server failing to communicate with the session. for some maps, when you try to launch session you just get a generic “cook error” message, with no asset/actor in particular identified. however, when you create a private code, it will fail, and flag which asset/actor is having the problem. once the validation issues are corrected, sessions will launch as expected.
however on some other maps, private sessions will be created as normal, and edit sessions still will fail to connect
so it seems to be 2 different failure modes with sessions