Maximum PVR playbacks with 4K PVR?

I have the PureFibre Gigabit plan. On my phone I measure 364 Mbps download & 249 Mbps upload using the Telus Connect app.

My router is an Actiontec T3200M. There are 4 TVs connected with 3 Arris 5602 boxes and an Arris 5662 PVR box. Two of those boxes are set up for 2160 for the 4K TVs. The other two boxes are set up for 1080p.  When the problem is exhibited only 2 TVs are on.  Both are using Arris 5602 boxes.  The 1st TV is watching an HD recording.  The 2nd TV is unable to watch a 4K recording.

I rebooted the Arris 5602 box that would not let me play the 4k PVR recording. No change. I then went to play this video on the 5662 box which is set for 1080p output. This time the 4K recording played. I immediately went back to the original 5602 box to play the 4K recording. No dice. I was getting the same message as before even though this recording would play on the 1080p box.

I waited until the 1st TV that was watching an HD recording to stop. Once this box stopped watching the HD recording I returned to the 4K box to watch the 4K recording and I was able to watch this recording.

I will try running a few more tests today to see if I can watch multiple recordings at once.