Constant Encoding Failure with a Strange Ending

Another problem in this long list of Media Encoder Issues.

I have been trying for hours to render a Premiere Pro project which has multiple After FX dynamic links (intro, lower thirds, outtro etc.). I'm on Windows 11, Dell XPS 8940, Intel i9-10900 3.70 GHz, latest version of all apps, NVidia GForce RTX 2060 graphics, fast SSD drives and 32 Gb of RAM.

The sequence won't render from AME (or direct from PP for that matter) and stops on the first frame (as far as I can tell) after the openning After FX intro.

I tried everything - Playback engine settings in all types, replacing video files, updating drivers, uninstalling and reinstalling the software, clearinbg caches, swapping drives, removing effects, rendering to a different drives, disabling parallel encoding and I even sang a Christmas song to Adobe Premiere in 5 different languages.

All to no avail UNTIL...

I pre-rendered the After FX intro to a QuickTime file (it has to have an alpha channel at the end) and boom, it worked.

So on the hand I'm happy but on the other, I'm trying to figure out what the f*&% is going on.

Do any of your super experts have an idea?

Thanks so much.
Martin