So, how did you solve the maze this run?
The solve button worked perfectly for me, as expected, a couple of days ago.
404 is a "not found" response code.
So, either KoL changed the URLs required to access the maze (extremely unlikely) or it was a transient glitch in KoL's server.
P.S. you certainly DO have a "session log" - but that would not help. Would would help is a "debug log".
I'm going to predict that you cannot reproduce this, but until you report back here one way or another, this goes to "waiting for information".