Just for transparency, I also sent this info to support via email directly, as after I made this post, I noticed a pinned forum post suggesting I should not use this as a substitute for contacting support directly. So, if by helping me here, you'll just be duplicating work, then feel free to ignore the below.
EDIT: sorry I should have mentioned, the video I uploaded as an example is, I believe, 4k@60. But, I've certainly reproduced at 1080p@60.
I made a demo video showing what happens: https://drive.google.com/file/d/1TALVI6efE5Zhf7vel_b-CsctfwN1y0k_/view?usp=sharing
I also uploaded the source video that I added to the VideoPad timeline to elicit the behaviour: https://drive.google.com/file/d/1kCJGmwJGRlAF3nFalLwoP7O-O9GQQahr/view?usp=sharing
The file that I added to the timeline to elicit the bad behaviour has the following properties you requested.
File format: MP4
Size: 46MB
Length: 3 minutes, 5 seconds
As you'll see in the demo video, processing this file used 100% of 64 CPUs, and 100% of free memory (20GB), grinding my computer to a halt.
I exited non-essential programs before triggering the starting VideoPad and triggering the behaviour. I was only running Chrome, OBS to record, NVidia's webcam background filter (as part of my OBS recording setup), and MS Teams in the background. I have task manager open so you can see what else is running / happening in the video in real time.
I can easily reproduce this over and over even with very small videos. Once a video is first processed and is cached, the behaviour no longer happens (unless I clear the cache).