I updated a site to Joomla 3.7 recently and it seemed to break the front end site. I could get into the back end OK, but every time I tried to get into the front end, it gave me an error about too many redirects. I spent quite a bit of time searching for fixes for that and most of them talked about problems with the .htaccess file or the SEO settings. I spent way to much time troubleshooting with that. Doing more searching, I found a few other references to my problems none of which helped, but eventually I found my way to this article. It was the exact problem I was having and also provided the fix.
"If you really must set your HOMEPAGE as registered, then you MUST have a different menu item, of type public, of type Login Form, so that users can be redirected to that menu item (Itemid) in order to login."
Essentially, some change in the 3.7 update makes it so that the Login has to be a publicly accessible. I have several sites I work with and all the others were just fine, my problem site has everything with a minimum security of Registered. To get to the site required a person to be registered, when Joomla detects that the user is not registered, it redirects to the login module. Since the Login module required a user to be registered, it would redirect to the Login module, so the redirects would not end. Once I made the Login module 'public' the redirect was able to open up the Login module and thus allowed a successful Login.
Kind of a strange problem and all the errors and symptoms didn't really point me in the right direction to solve it. I'm not a Joomla expert so if maybe I was, it would have been easier to troubleshoot, but as someone looking at Joomla to be pretty straight-forward as long as I don't go crazy with making changes, this was a frustrating problem to try and resolve. I'm still a fan of Joomla and it seems to get better all the time, but these updates all seem to introduce little nuances that are frustrating to figure out when they break something that was working before.