My problem is that I can't simply share any site with any user. A couple of weeks ago I started creating a site collection and adding content to it. Once finished, I duplicated this site collection into different content databases for every client's department.
Today, I thought everything was fine, until I noticed that when I try to share a site with any user, that user always receives "Sorry, this site hasn't been shared with you", which is false, I shared it to that user.
I googled and have tried everything but I can't solve this. I did a simple test, which was to create a completely new site collection, share it with a normal user, and user can, of course, access. If I stop sharing, user cannot access to this test site collection. ¿WTF?.
So, with that test, my guess has been that the problem is in my original site collection. Consequently, every duplicated site collection has the same problem, and I don't know why the original site collection has this problem.
How can I solve this? Anything to test or debug? This is a really weird and worrying problem because I cannot simply share a site with a user in my SharePoint project, which has taken me a many hours to create.