It keeps forgetting for me too. That is to say, in my mobile browser and desktop browser I opt out of the redesign in favor of the old.reddit.com design, but about once per month it'll just revert back to the redesign. I don't think my cookies are being cleared because I'll stay logged in and I've never found any other setting that flips in the same way, it is only the Redesign opt-out that does this.

I don't know how to explain why many people say "this never happens to me" and other people say "this happens frequently."

While I'm on the subject, another grey pattern the article missed is the button to opt out of the redesign on mobile. When clicking the hamburger menu there used to be a button at the bottom called (iirc) "Opt out of Redesign." The same option exists today except they've moved it into a Settings submenu and renamed it "Request desktop site" which implies it's a temporary change.

Lastly, if you search you'll find threads where people say the web pages are sometimes rendered without any opt out button. I just opened an incognito window to test this and I simply cannot find a button to revert to the old design, even when using my mobile browser's Desktop Mode. So unless a visitor knows about old.reddit.com they are forced to use the new design.