There was a delay that @dankcushions mentioned regarding RA 1.7.7 specific to ARM devices. I know at one point the team mentioned they were waiting to release RetroPie 4.5 until 1.7.7 was released, but I think they scrapped that idea when the ARM issue was discovered. I'm basing this all off of memory reading some of the threads here about a month back.
ETA: I think the bug has been fixed, but again I'm just going off of memory.