I can pass this information on to see if there are any issues. When you do queue as a group, the system prioritizes putting you together with other groups, the same way it prioritizes putting you together with people who are solo while you queue solo. After some time, the search for viable players will expand until the rest of the slots are filled. This system should make sure you are not in a queue for an extremely long time.
/gabelikes
We've completed full boss runs (even without fast travel) for a 3 man group at 10:30 PM CST without the group getting into PvP survival. I don't think it's switching to mix groups like you're saying @Ubi-Gabelikes I think it's just waiting until our 3 fit with 21 other players for group.
Also, what this is causing, is people will group once they enter solo, whether PvE or PvP. PvE it's no big issue, but in PvP the solo queue should disable grouping in the instance.