Im getting these two errors and my site is stuck keeps giving me a 500 error.

The 2 errors are :

PHP Warning:  call_user_func_array() expects parameter 1 to be a valid 
callback, function 'wp_ob_end_flush_all' not found or invalid function name in 
/public_html/wp-includes/class-wp-hook.php on line 286


PHP Fatal error:  Call to undefined function wp_suspend_cache_addition() in 
/public_html/wp-includes/cache.php on line 402

Weird note: I accidentally moved all the files into a subdirectory ie. /public_html/examplefolder/allwordpressfiles. and the site worked (without any of the images or links working obviously) but it didn't return a 500 error.

So is there something wrong with my public_html folder I check permissions and they were 755.