Hi there! There's currently a Known Issue with premade groups of 4 when queuing for Group Finder. Unfortunately, this is manifesting in several ways, as you noted here. We apologize for the inconvenience and are working on getting it resolved; due to the way the issue is manifesting, the team is taking extra time in testing the fix once it's ready. We'll keep you updated when more information as it becomes available.
I've encountered it also and have threads in other sections of the forums about this. As an aside it's not just 4 man pre-mades for tier 1 HM FPs. 8 man pre-mades for story mode Ops done via group finder are just as bugged. I think I read that 4 man pre-mades for easy mode level 50 FP's are again bugged and not giving out the coms one would get for that tier of FP.