That was it! Saving and loading the cookie jar, apparently, wasn't actually sending the saved cookie in the next request. I'm not sure why, but I'm just manually setting the cookie header before the form submit and that solves the session problem.

In reply to Re^2: Maintaining sessions with WWW::Mechanize across script instances? by EvanK
in thread Maintaining sessions with WWW::Mechanize across script instances? by EvanK

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