Complete and random breakdown of blog, super cache may be involved

Here’s the basics:

• My blog, https://www.benparr.com , was running fine this morning. I made no edits to the template, design, or even posts. I take a shower and when I return, I’m greeted with the following error:
  

  Warning: Cannot modify header information – headers already sent by (output started at /home/.castor/lifeisfree/benparr.com/wp-includes/theme.php:10) in /home/.castor/lifeisfree/benparr.com/wp-content/plugins/wp-super-cache/wp-cache- phase2.php on line 39

  Fatal error: Call to undefined function get_template_directory() in /home/.castor/lifeisfree/benparr.com/wp-settings.php on line 542

• I could not get to the admin panel, so I emailed Dreamhost, who is my hosting provider. No response, but early afternoon I find I can log into the admin panel and the error has changed to this:
  

  Fatal error: Call to undefined function locate_template() in /home/.castor/lifeisfree/benparr.com/wp-includes/general-template.php on line 34

• But if I switched to another browser NOT logged into the admin, the error disappeared and my blog was there. But the most recent two posts were NOT on the front page of my blog, ALTHOUGH they are still in the system.
• So to fix this, I’ve turned off WP Super Cache (apparently there’s an issue with my trailing slashes that creates a bug in WP Super Cache?), I try unpublishing those blog posts in case they have something to do with it, I look at a mess of things, but I’m stuck. So please, help, I’d love you forever, give you a shout-out, who knows what.

Thanks.

– Ben
https://benparr.com
https://mashable.com/author/ben-parr