Sure, understood - so maybe consider uploading something to a file hosting site (OneDrive, Dropbox, etc…) and just attach a ‘link’ to that location to download from…?
And that being the case, it would be great to get them some output to examine - see if they can do something about it…
As I maybe indicated earlier, problems can manifest from device to device - i.e. output from one Sony A7c Mark I camera might not show an issue, whereas yours, does… Honestly these things can be that fickle.
The only real known state right now is that your Sony A7c Mark I does show a problem. Lets start there.