I understand what you are doing.
when uploading to YouTube directly from PD an intermediate file will be made. Have you checked that file to see whether the correct audio has been made or not?
Also from this forum I understand that there may be something wrong with the direct upload to YouTube. This may have to do with changes in PD, but can also be because of changes in the YouTube API. Checking the production result in the intermediate file will help you and CL development to determine how to solve this problem.
If production to local disk takes the correct audio channel I suggest that you use the YT file upload instead until CL has resolved the issue.
And to initiate that, I suggest that you file a error report together with the additional information discussed and a link to this foru: page.
That is I guess what can be done right now. Let us know how this continues!