Please don't do this (see attachment). I totally avoid sites that do this because it is so cumbersome to review threads.

See the little 'Display Modes' button at top right of thread? Click on it and choose 'Linear mode' ;)

It's not the forum - it's only the setting you are using!

Yes, it is a user-based option. You can select to view threads the linear way or the threaded way. :)

I didn't change anything when it started happening, nor did I make any changes when it went back to normal several hours later. I'm not sure what happened, but thanks for letting me know about that 'Display Modes' button, I never noticed it before.