I have a v5 with a 3.2 " Nextion and CEC version 1.2. I do not have the Memory Manager version as I am on the road for business right now. With the above I have been able to directly connect to the Nano with the MicroUSB cable direct to the Nano port. When I read about running cables to the rear panel, I wander if there is another factor in the mix, like a case with rear connectors and/or aux boards for ease of wiring. To really know where the issue is, we need to list all of the non-HFSignals mods in addition to the CEC mod so that the problem can be clearly defined. I have read of multiple threads where the issue was traced to a case mod that gets between the uBitx board and the rest of the world.
With the above understanding, PLEASE be sure to list ALL non-stock mods so that we can compare apples to apples. It may be that there is a know issue with something as simple as a wiring error on a case kit that has come up in the recent topics. This type of problem can only be solved if all of the information about the rig is known.
Now to better articulate my setup, It is all stock EXCEPT for the CEC/Nextion display AND a power drop resistor on the 12 volt line feeding the 5volt regulator on the Raduino board. There is a know power issue with running the stock Raduino board with more than a 2.8" Nextion display. The total power required is more than the regulator can handle with more than 12 volts suppiled to the the main board (the PA can be higher with out this issue). I also added two 1n4xxx diodes between the 13.8 volts supplied by my power supply and the RED wire on the uBITX board. This was done to keep the voltage supplied to the main board close to 12 volts (i have since measured 11.9 volts under power).
I have gone to this level of detail to explain my setup to give you an example of the level of detail that is needed for us to help. We have not all used the same setup when building our rigs.
Apologize on being long winded on the need for details, however it is for your best interest. Wrong information can lead to wrong diagnosis and ultimate board failures.