No horizontal scroll in Safari. Bug, or pref?

Question

Mac Pro 5,1 Mojave, Safari [latest] 14.1

Since the last Safari update in the last week, I've lost the ability to shift/scroll to move horizontally.
Fine in Chrome, Finder etc, this seems to just be Safari. Did a pref slip somewhere? I've never really tried to find if this is a pref, I thought it 'just happened'.

If it's a bug I'll report it, but I'd like to know if I missed a pref.

Screenshot hopefully wide enough to display this. Click the image, then if you see a magnifying glass with a + in it when you hover your cursor over the letters, click again so it goes beyond your window size [or repeatedly tap Cmd ⌘ + until it no longer fits the window].
Hold Shift & scroll mouse wheel.

It would be interesting to know if this affects trackpads too, but I don't have one to test.

Answer 1

It's an issue with AdGuard, specifically the Web Annoyances Ultralist.

Reported to the developers in https://github.com/AdguardTeam/AdguardFilters/issues/82833

with a dev response

Ok, better disable this filter. It can break something in Safari, also our filters compiler has one issue AdguardTeam/SafariConverterLib#21 After release which will contain the fix for problem above, you can try that filter again.

I have that filter disabled for now & will test again after the next release.