Quick solution: Try to manipulate the faders “holding” the knobs with two fingers, touching the most area possible of knob. 
I have just posted on this issue. Sick and tired of it now my Mackie works on the same midi setup with 2 other daws without ANY issues at all but it will not work right in Cubase 9.5.20 never had this issue before. Steinberg so far don’t seem to be interested
Many users have posted to say that it is working correctly on their system. If it was broken there would be many reports saying so. I understand and sympathize with your frustration, but you should go step by step through the setup of the MCU and make sure you have it correct. For example, disconnect all midi devices, then restart your machine. Now connect the MCU and Run Cubase.
Please note that the fact of it working in other daws does not rule out an error in the Cubase setup.
Also make sure you have done what Raphie has suggested:
Thank you so much Steve I did not understand exclude the ports. I have done some digging and now I know that I can deactivate other midi inputs and outputs. I always thought they were fixed for some reason. I will have another go tomorrow and see if I can once and for all resolves the matter. Thanks again for clarifying what I just was not understanding.
Hi Steve,
I have excluded all ports in Cubase and no midi was coming back to the Mackie for it to work? I switched on the port for only the Mackie and the same issue is still there! I have never had this problem before and it’s doing my head in am trying everything but seems there is a loop happening causing overflow of info to the Mackie.
Hi,
The goal is not exclude the ports completely. Just remove the Input MIDI Port from the ‘All MIDI Inputs’.
But, tell us , what exactly occurs ?