I can't search this thread, but I'd add a few causes:
For pure eye strain:
status lights such as power lights which are too bright, in addition to the screen
reflected images on the screen
background images on the page
red and/or blue lights
tiny text
hard to read fonts - I find Google search results unreadable in their default font
* fonts which make it hard to find your place after your eyes lose focus or switch focus from one to the other - I find Andika works for me, but Comic Sans works best for some people.
For photosensitivity, or at least my photosensitivity:
Flashing and blinking status lights
Flashing and blinking objects on the screen
Flicker again - old flourescent lights can be an issue at 120 hz, and are blinding at 60 hz as they burn out.
Jitter animation
Zooming animation - one of my most reliable migraine triggers
Parallax, carousel animation
Pendulum, metronome, Firefox Quantum tab throbber animation
in-window pop-ups
sheer between scrolling and non-scrolling elements - especially close to the middle of the screen, and cutting across patterns, so Twitter threads are a good bad example
page elements changing shape
although most of these are software or page layout issues, it's possible* that changing refresh rates or other hardware characteristics would change sensitivity...?