Huh, how weird. idkfa was experiencing some pretty severe downtime on Thursday / Friday, after which there were... subtle changes on my host system. These changes tell me that the idkfa hosts disabled certain features of PHP (the language idkfa is written in), likely because they found other users abusing them.

As such, during these downtimes, it must have been that the idkfa cache got borked while that thread was created. And the case for "no cache files for a thread, even though it's impossible for them not to exist" suddenly issued an error message that it couldn't find anything (the "invalid argument" error). And that message came before I could do the proper "redirecting," violating a constraint of the HTTP protocol, and thus kicking your browser to the manual redirect page.

Thanks for the heads up.