Personally I have not experienced any issues with mxf files from a range of cameras in Resolve including the FS7ii so I’m not sure what might be going on. I’m monitoring audio via the Fairlight CC2 card or prior to that the Decklink 4k card. How are you monitoring audio?
Also what is the sample rate and bit depth of the problem files? Number of tracks etc. Sony cameras are annoying in that they record so many audio tracks, even when they are silent. Just for interest try going to clip attributes on one of these problem files and turn off all but tracks with audio to see if it is related to having all those useless tracks trying to play.