Sorry to hear that, it sounds like you will need to restore your forum from backup
After upgrading to 1.18.6, the login button on the top right of the home page does not function. Strangely, when I try to login to reply while on the talk page, the login page opens.
@kurulumu-net try rebuild and restart
@kurulumu-net anything in the browser console ?
@phenomlab no there is no console error.
@kurulumu-net Odd. I'm not able to reproduce this. Have you tried disabling plugins to see if any of those are the culprit ?