"...However, when I tried it in VoiceOver, I discovered he was
correct. As soon as you reach a "week" indicator, like "Week 1", a window
would appear at the top left of the screen and Safari/VoiceOver would be stuck.
I had to kill the VoiceOver process to get it back.
[...]
I then realized
that the problematic area was embedded in a span with a CSS class of
"accesshide". Removing the span with its class from the page solved the
problem. It was the CSS class that was somehow at fault. "

To summarise, the tutor who reported this found that by making the number 10,000 instead of 100,000 this stopped Safari breaking. Yay 16-bit integer?

I found a related problem when making accesshide links appear, which is that sometimes the browser scrolls to top. It is better to use left or right for this approach. Moodle code was changed to use top because of RTL languages, however, this is unnecessary as we can use .dir-rtl. (Change tested in RTL language.)