...which I confirmed by dumping the response headers

Have you also checked the request headers for the second invocation (e.g. using wireshark) to see if the old session ID is actually being sent.  This might help to narrow down on where/when it is "getting lost".

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

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