It is frustrating that the hardware can play 1080p60 but it rejects anything above level 4.1. It is probably because cannot handle the max bitrate of level 4.2.
Forcing level 4.1 is a decent work around, I suspect many devices that refuse to play 4.2 or higher have hardware that can successfully play lower bitrate 1080p60. I do hate recommending anyone create out of spec video but this case seems to require it and is also unlikely to do too much damage.
