I just spot-checked your Alaskan block groups, and I don't see the values you list in the ACS 2015. That is, there's no county 02270 for those block groups to be in. 02275 is Wrangell City and Borough, Alaska.
Spot checking the two for CA, I don't find those in the ACS either.
(using this Factfinder page
factfinder.census.gov/.../0500000US06037.15000) 060378002043
This tract only seems to have two block groups,
060379304011
There doesn't seem to be any tract 9304 in LA County, let alone 9304.01
How did you come by the ACS data you're trying to join?