As of a few minutes ago old.reddit.com now seems to requre logging in to access it.
Shame as it was still the best place to browse for info about some niche interests.
Edit: Seems like they might be testing the change as it is hit or miss at the moment.
Edit: Adding this to My flilters in uBlock Origin seems to fix the issue for the time being:
||reddit.com^$header=referer:
My cookies for Reddit are locked and have been for a while, so maybe this is it? Doubt it, though.