Some observations that I wanted to share. I'm in the habit of uploading my BMPCC 1080p footage in Ultra HD 4K on YouTube, using QuickTime as a wrapper and DNxHR HQ as a codec when creating a render in the Delivery page of DaVinci Resolve.
When doing that render in Resolve 12.5.3, although it took all day to do the upload, I succeded using Firefox (my preferred browser). But after upgrading to 12.5.4 YouTube crashed on me after less than 30 minutes on each try, regardless of the size of the file. It only accepted 1080p HD.
I have made several attempts for the past weeks to no avail. My brilliant son came up with the idea to switch to Google Chrome, thinking that as YouTube nowadays is an extension of Google it could perhaps be more compatible. I tried it out starting yesterday. And it didn't crash.
So the conclusion is that, regardless if Resolve 12.5.4 has some issues with uploading Ultra HD 4K to YouTube or not, it is obvious that Google Chrome is a more stable browser compared to Firefox when you want to upload Ultra HD to YouTube. Don't know how Explorer works out but I generally dislike it as a universal browser.
If you have any comments or observations that corroborates mine, or disproves them, please share them here.