Two days ago I went to start my battle quests, then realized I wanted to battle the new throwback challengers first. When I clicked the "Battle with Defaults" button, though, I got a page with only the message "You have been directed here from the wrong place!" below the battle menu. Since then, every battle I have tried to enter (throwback or not, BQ or not, default weapons or not) has given me the same message, except the one for which I switched to a Macbook running Chrome. I hadn't played in a while previously and am not sure exactly how long this has gone on.

I am running Pale Moon 27.3.0 (a Firefox fork) on 4.10.10-1 Arch Linux, last updated the browser on May 18, and do not recall whether I have battled since. (In the past, this OS, browser, and add-on setup has worked just fine.) Although it seems possible that this is a PM issue, I cannot submit a useful bug report to the developers if I have no information about what is actually going wrong. What causes this error to be displayed?

For me it's: "That battle doesn't exist." Got that 3 times and ikr. :v

No; I isolated the problem to a missing HTTP referer and turned them on (I'd disabled them as a privacy measure).

IIRC this predated the battle UI update, so may or may not still occur; I can't check until tomorrow, but it should be easy for you guys to try if you're in a hurry.