See Kudpung's chart:
No one seems to know exactly why this is the case, but we should make sure it isn't due to a software change. Is there any reason why either:
- more articles would be set as unreviewed than previously (for example, we include redirects when we didn't before [purely hypothetical])
- the page patrolling interfaces aren't working correctly (for example, reviewers are not able to successfully mark pages as reviewed)
- or, the statistics are wrong (never trust your assumptions)
One possible cause is https://gerrit.wikimedia.org/r/#/c/272142/, which switched around a bunch of the UI elements in the reviewing interface, including the "mark as reviewed" button, replacing it with a "skip" button instead. (This has since been reverted.)
Are there any other changes to the software that could have caused such a dramatic rise in unreviewed pages?