Saw this posted on another site. Don't know if it does or doesn't work because haven't tested...Yet.
"For all who are having this issue (as I am) you can set your Hopper 3 to record the 4k channel and then using options > TV Activity can select the tuner that is recording the 4K channel on your Joey. I am currently watching speed skating in glorious 4K HDR on my 4K Joey. But I really hope they fix this bull**** soon. So dumb since I know channel 540 works on the Joey since I have watched Planet Earth II and college football in 4k with no issues last year."
"For all who are having this issue (as I am) you can set your Hopper 3 to record the 4k channel and then using options > TV Activity can select the tuner that is recording the 4K channel on your Joey. I am currently watching speed skating in glorious 4K HDR on my 4K Joey. But I really hope they fix this bull**** soon. So dumb since I know channel 540 works on the Joey since I have watched Planet Earth II and college football in 4k with no issues last year."