I have seen other topics that discuss this same problem. I don’t know why it works now, but apparently it is an issue with your plugin for some short period of time after the plugin is activated, but only for those who are not logged in.
I’m happy that it works and I hope it continues to work. But last night I asked several people from various parts of the world to test it and all of them had the same problem I had when I was not logged in. I tested it on my theme and with the twenty fifteen theme. I tested it after disabling some, but not all of my plugins (if it is a conflict with some of the most popular plugins in the world, then it is a problem with your plugin, not theirs).
This is no longer a problem for me, but I am quite sure you will continue to see it is a problem for others.
Thank you for your reply.