Hi,

Recently I have some problem with K2 front end. ...
1. When I login to edit an article, the close button doesn't not work. You can not close the pop upp window.
2. If I save the article, it brings up a new login page with security key (see b2 and I have not active any security key). I can reload the page and article has saved.

I have not these problems before and don't know why it happens. Hopefully you guys can help me out.

k2 version 2.7.1 and joomla v 3.6.5

screenshot here imgur.com/a/LaSfV

Thank in advance.

Hello,

Have you enabled any other extensions?
Any new security rules?

As I know we have not enabled any extensions or new security rules....

The closing might most likely be a JS error.
Open the console tab of your developer tools and look for any errors.

Are you using any caching extensions?