I was in the expanse doing the Defense against Fed Spies quest by myself and got to 1/3 complete when a friend joined me in party and came into the instance. We did about 3 more maps and I noticed my counter was still at 2/3 now. Another friend joined us and we did another clear and his quest went to 1/3 but the other two, myself included, stayed at 2/3. Now in Beta, we could join each other and it didn't matter what party member was where in the progression. We all were able to progress and turn completed quests in. Did something change now that ALL party members have to be at the SAME progression? We are about to see if this is true but thought I'd post during the ever FUN 6 minute reset.
Update = Well the 3rd guy to join us went from 0/3 to 3/3 and complete. Me and the other guy were stuck at 2/3 still. YAY for waste o'time.