Anyone can register? unless…..

The “register” link keeps removing itself, and my visitors cant add a comment due to this.

In settings, I check the boxes next to membership, __anyone can register, and ___Users must be registered and loggind in to comment.

Then I come back in a day or two, and the ___anyone can register is
unchecked, and also the “register” text link is gone.

Why does it do that, and how can I keep the “register” link always available?

David