Jumpy [B&W] composite video signal from 1974 dumb terminal

[MightyFrame]

I'm not sure if this might be beyond the scope of this forum, so if it is, please forgive me.

I'm very much a newbie to the technical understandings of vintage video, and I'm hoping that some of the experts here can point me in the right direction, maybe give me some pointers or explain what I might be doing wrong here.

Basically, I'm looking at a B&W composite video signal coming from a very rare vintage dumb terminal from about 1974. I'm using a USB composite video capture device to view it, but the video signal is very jumpy.

It's apparently a PAL signal at 625 lines, but as far as my research shows, this modern equipment should be able to handle a standard PAL composite video signal no problem, without this jumpiness.

Here's a very detailed video showing the problem, and what I hope is [too much?] information about everything I know about it, and can possibly share up to this point.
Video of the problem detail:
https://youtu.be/nTPZRe_TK2U

If you're interested in diving into this, I very much appreciate your willingness to watch this video.

Some of the resources I show in the video are hyperlinked right here for convenience:

My page with all technicals about the terminal
http://bit.ly/2XpxETd

Terminal Motherboard Schematics (that create the composite video signal out)
http://bit.ly/2r1m0Sj

Motorola Monitor-TV Chassis Schmetics
http://bit.ly/35dx11L

Logic Capture File of the signal for 8 seconds
http://bit.ly/2Xso8i3

Saleae 1.1.15 install (for Windows, if needed, to view the logic capture file)
http://bit.ly/2NUJjWU

Video of the actual CRT chassis assembly that was made for this terminal:
https://www.youtube.com/watch?v=qPjS...ature=emb_logo

Video Capture Card StarTech.com SVID2USB23
http://bit.ly/32S2l4p

Thanks so much everyone, and I really appreciate your help and feedback on this!

Best always,
AJ