I’m having similar problems and have been since I updated to Cubase 7.5.10 (up to v7.5.20 with these symptoms). i.e. MCU 8 would stop controlling Cubase at some point in time. No error messages, no PC lock but in my case, sometimes my MCU 8 would loose Track/Channel information in the MCU’s LED bar and showed no Cubase information. Like Ted’s issue, MCU 8 does continue to show Time/Tempo information if I use Cubase Transport Controls. Sometimes, if the LED bar did NOT loose Track info, the MCU 8 would resume working after some elapsed time.
I updated to Cubase 7.5.30 and now, the MCU won’t work in Cubase. Neither 64-Bit or 32-Bit versions. It won’t work not even at the beginning. It does continue to show Time/Tempo information but does not show any Track/Channel data.
I currently have a trouble ticket in for another issue that surfaced after I updated (LoopMash Fx has a Blank Quantize Screen). I do think the MCU 8 issue is Cubase but- don’t know if the LoopMash issue is related. Love to hear some ideas on fixing this. 