Hello,
I've exactly the same issue. My Rode Videomic pro Stereo, won't connect correctly. With mit EOS 7D2 its working without any issue. In the 5D4 sometimes I only have the left channel.. sometimes it switches to the internal mic.. i played arround in the calibration settings. On that screen you lower the "input" (( in the first quarter) and change my rode to +20db.. with that setting you'll see every change between external and internaml mic cause the internal is not that loud than the external rode.
So, i'll sent my 5d to a CPS office. Lets see what happens now.. I'll update you as soon as I've it back.
cheers
spl1