Warning: Don't set the UserPage prefix to blank or you can't edit pages.
Big Shout Out to Louis-Philippe who found the reason no-one could edit any pages on my Tiki.
The user page prefix (I don't know if you use those) was empty, leading to some confusion in how to handle the page. I had actually seen and fixed this issue before. The fix will be included in 6.2 which should be out shortly. Until then, I changed the configuration back to a non-empty value.
Further, it appears the prefix must end in a colon or no one can create new pages. I know. It's weird.
Cheers,
-Kent