When you say “My cofounder gets in just fine” do you mean from the same machine? If so, than that’s really weird and may be related to your account. If not, then there a many things that could cause the issue (local state, browser extensions, operating system firewalls, routing rules, network configuration, …). Something that may help to narrow the problem down is to try to log in from a different machine (assuming you have access to one).
Since you are observing the same issue with different browsers, it’s probably not related to cookies or local storage (which, in my personal experience, is what causes such issues most often). Still it wouldn’t hurt to try to clear the cookies or try in incognito mode.
If you still have the issue can you please check your browser’s console for errors. Posting those, as well as the actual network log (between which URLs it loops) could help identify the issue. I’m afraid without more detailed information it’ll be really hard to help you.
Jocelyn @ Pinecone looping back – I was curious and asked out support team. they said that on occasions where they’ve seen this happen, its almost always a machine or browser issue
Milen’s given a solid response upthread, so I’m marking that as the solution. Let us know how it pans out for you to try from a different setup, and happy coding