Problem with OceanWP Popup Login

I use oceanWP theme and one of their premium extension- Ocean Pop Up login.

One of my users reported that he couldn’t login or reset password because he was getting an “session token expired” message. So I changed his password from admin backend and then he was able to login with the new password. But after a while, he was forced logged out and then he couldn’t login because of the same error message. See the screenshot attached.

I have tried different browsers, different users and different roles for logging in, but still they show the same error:

Session token has expired, please reload the page and try again

I am posting this here because I couldn’t find any plugin conflict and the problem was gone once I deleted the WP Fastest Cache and Minified CSS. After a few days the problem was there again (maybe the cache grew?) and as I cleared cache and minified css, it was solved again.

Screenshot of the problem and my wp fastest cache settings. I use autoptimize to optimize CSS HTML and JS, so I use only the caching features of your plugin.

The page I need help with: [log in to see the link]