Can't select the Text Tab in Posts after 4.3 update

Pretty much what the title says. I can only select the Visual tab. When I try to click the text tab it just makes a blue highlight but doesn’t switch to text.

I’ve tried disabling all plugins and changing themes. No luck.

Also tried setting debug to true in the config file. No luck.

Oddly, when I go to Users>Admin>Edit and disable visual editor I can then write in text for posts.

But obviously, I would like to be able to switch between the two freely.