[quote="ShutterMonkey"]
Update: when I change the resolution from 2160 x 3840 to 1080 x 1920, the export works.
But I still don't understand why the exact same edit
withOUT the vertical crop at 3840 x 2160 Ultra HD, there's no problems exporting. Only when I opt for "Use Vertical Resolution", this happens.
/quote]
Do you know for a fact the hardware encoder can encode 2160x3840?
It may work differently to Nvidia encoders that encode in a square format, 4096x4096 or 8192x8192, so that means there would be no problem with encoding 3840x2160 or 2160x3840 as both resolutions fit within 4096x4096.
How about the transcoder Handbrake, does it work at hardware encoding 2160x3840
https://handbrake.fr/downloads.php