I have just bought a Canon 6D Mark 2 and found that when I opened my RAW file in AP the colours not as the original file on my iMac using Mojave. I am not sure if that is the same problem here. I, however, contacted Affinity and was given the following instruction which works for me:
With the RAW image opened in Develop Persona go to menu View ▸ Assistant Manager... and change the first dropdown (RAW Engine) to Apple (Core Image Raw). Reload the image for the new setting to take effect. The RAW file should now load correctly
The first picture is what I saw before the change and the second after. Hope this may answer your problem. I haven't yet got the second picture exactly how I want it but this was a test picture to make sure it worked.