I am running a 5th project right now with <forms> handling enabled.
And I see major memory spiking there...
I am guess there's a huge list of URLs that build up somewhere to be listed/analyzed.
Imagine you have 3 options each of 100 choices (e.g. age or whatever). That gives 100*100*100 = 1 million URLs that get queued for test/lookup (and then listed and/or analyzed)
I have not received any email from you yet, but my guess is above is to blame. Quite possibly 2.x did not support <forms> related HTML tags as well as 3.x does meaning 2.x possibly did not catch as many unique combinations. This is my *best* guess sofar. But of course I can't 100% rule out a bug somewhere in the <forms> code. I will keep my eye on it
Maybe I will add a debug mode info, so one can see amount of URLs queued for lookup/test (when A1SG tests a queued URL it first check if the URL already has been analyzed/listed already. If it has, A1SG just updates links-to/linked-by counts and similar data)