I've been having issues with archive.is over the last month or so and I know others have had the same issue. Back when when it worked properly I noticed that links would often redirect to a different top level domain. It seems that was a way to keep the site working and for whatever reason the TLD switching stopped working. But you can change the TLD in URL manually and every time I've tried that at least one of them will work. For example if archive.is/xyz doesn't work try archive.ph/xyz.

Here's the list of TLDs I've seen:

.is .ph .vn .md

It's kind of a pain especially on mobile but it is a solution if you care enough to see the archive.