This has been going on for some time now & I'm annoyed that PD hasn't released a patch - I'm running PD8.
I ran a trial version of PD11, it worked fine - once then it started crashing partway through rendering - so I have to uninstall/reinstall, I get 1 upload & the next file crashes - so I guess my old comp can't run PD11.
Only thing that works for me is having to type "yt:stretch=4:3" AND "yt:stretch=16:9" in the tags on every upload - a real PITA.
If I do one without the other, I always get the black lines so I found I have to type both!