Hi Vicki!
The behavior you're describing should *) not be related with the cookie lifetime. Depending on which browser / browser version and OS and password manager you're using, autosubmit is a known thing. I found articles from 2019 about Safari starting to do this. I'll ask around on our Discord channel if anyone else has noticed something. Aside from that, it can just be an unlucky coincidence with a tool update that introduced this behavior.
Michael
*) There is no relationship between cookie lifetime and an automatic form submission in the specs and the cookies only come into play after the form is submitted. That said, weird stuff can always get added to vital software.