Please post a link to the offending page.
The aliId is the form data cache key. It exists on pages that have been loaded after a successful submit. So, as you've noted, that means the Thank You page then submits the form again.
My initial guess is you have some logic designed to auto-submit the form under some circumstances that's misfiring.
Or, of course, it could be that if you use the same page as the Thank You page without changing the page contents at all, the person doesn't think their form went anywhere (a not illogical assumption) and fills it out again.
There isn't any one specific offending page, they all seem to be guilty. The most common form in general is this: https://www.millerheimangroup.com/training/advanced-selling/strategic-selling-with-perspective/
So here's the thing.
The intent of the custom ?aliId query parameter in the URL, because that only happens with the default (non-customized) behavior (or if you deliberately emulate that same behavior in custom JS).listener on your page is to stay on the same page without refreshing and show a Thank You message. Ergo, there should never be a pageview with the
However, the ?aliId and show the form again. That could well lead someone to think the form didn't do anything, as I mentioned.listener is added as part of a larger block of only semi-related code (starting on line 399) rather than standing alone. If any fatal error should happen in that code before the is added (it's only added at the very end) then the rest of the code will never execute. There are enough different functions in there that certainly something could go wrong under certain browser conditions. If that happens, the form will still submit, but it'll be using the default behavior -- which is to refresh the IFRAME with the
As for what in those 100 lines of code could sometimes, but not always, error out, it's hard to say. I see some very minor oversights (looking for fields starting with "utm" fields in the whole document, instead of just the current form, for example, and not securingas much as I'd like) but nothing that calls out as fragile. But I can all but guarantee that's what's happening: something else is erroring out, so the listener doesn't get overridden, so the end user thinks the form didn't get posted and tries again.