I’m having this issue as well but the workaround does not resolve it. I’m on Firefox on iOS. Having the same symptom where it redirects me to the login page but manually going to kagi.com works.
I’ve tried disabling the “close private tabs” setting, but that doesn’t change the behavior. In addition, the Github link says that it only occurs on the first tab opened when Firefox starts, but I seem to have it happen when I’m already using Firefox.