HR10-250 goes crazy when tuning to ESPNHD or UHD

Any ideas? After 3+ years of perfect operation, one of my HR10-250's hard drive died about 3 months ago. I bought a replacement drive and installed the InstantCake software and got my machine back up and running. It's been fine for 3 months, but for the past week or two, every time I tune to ESPN HD (73) or UHD (74), the HR10-250 starts to freeze, pixelate, screen goes black, etc. In general, it just stops functioning. If I change the channel, it will take forever but eventually change, and it works great on all other channels. From time to time, it will reboot itself when I tune to 73 or 74 before the channel change takes effect.

It's not a signal strength problem (signal is solid in the upper 70s) and I have no problems on my other HR10-250 in the next room.

ESPN HD is the channel I watch the most, so this is obviously a big issue for me.

Thanks in advance for any ideas or thoughts.