Yep, thanks Disston for the detective work - it appears that AdBlock in Chrome causes the same problem.
I wonder if this is a change on ADV's side? Like they block logging in for anyone with AdBlock enabled? This would mean ADV is about to go ad-supported...
Current: 93 R100GS, 04 XR650L
Prior: 73 CB350, 77 R100/7, 83 R100RT
I love every motorcycle I've owned and even some that I haven't.