I've been having these issues for a while, but whenever I have the wiki open on a browser window that's snapped to the left or right of my screen, I'm unable to pull up the left sidebar or click on the right side of the screen (except for opening the "Page tools" menu, which gets cut off on the left side in this state).
Topic on Talk:Main Page
From Elwiki
In terms of the pulling up the sidebars, I don't have a solution for that. For the right side being unclickable. Best I could recommend for now is not shrinking the window to the point both the left and right sidebars go away. It's only once left sidebar disappears you start having issues. Not exactly sure what the root cause of it, but I'll see if the guys more experienced with the backend of mediawiki could figure out the cause.
Okay, Ritsu found a way to fix the issues with the sidebars and area not being clickable for now.
