After installing wordpress 5.0 i got these errors:

Classic Editor is already installed. I hope, you can help me fast. :P

Error Code:

Uncaught Error: Call to undefined function excerpt_remove_blocks() in /var/www/wp-includes/formatting.php:3311 Stack trace: #0 /var/www/wp-includes/class-wp-hook.php(288): wp_trim_excerpt('<i>#Duisburg\xC2\xA0(...') #1 /var/www/wp-includes/plugin.php(203): WP_Hook->apply_filters('', Array) #2 /var/www/wp-includes/post-template.php(397): apply_filters('get_the_excerpt', '', Object(WP_Post)) #3 /var/www/wp-content/themes/soledad/content-magazine-2.php(87): get_the_excerpt() #4 /var/www/wp-content/themes/soledad/index.php(78): include('/var/www/wp-con...') #5 /var/www/wp-includes/template-loader.php(74): include('/var/www/wp-con...') #6 /var/www/wp-blog-header.php(19): require_once('/var/www/wp-inc...') #7 /var/www/index.php(17): require('/var/www/wp-blo...') #8 {main} thrown in /var/www/wp-includes/formatting.php on line 3311

Already tried.

In my case (not Similar to yours) Ι downgrade again back to WP 4.9.8 version and all my problems gone.

WP 5.0 is still Buggy.

Take a look here => https://pencidesign.ticksy.com/ticket/1812361/

New Install of WP 5.0 solved the Problem. ;)