wp-include files disappear

Try downloading WordPress again and delete then replace your copies of everything except the wp-config.php file and the /wp-content/ directory with fresh copies from the download. This will effectively replace all of your core files without damaging your content and settings. Some uploaders tend to be unreliable when overwriting files, so don’t forget to delete the original files before replacing them.

If that makes no difference, try manually resetting your plugins (no Dashboard access required). If that resolves the issue, reactivate each one individually until you find the cause.

If that does not resolve the issue, access your server via FTP or SFTP, navigate to /wp-content/themes/ and rename the directory of your currently active theme. This will force the default theme to activate and hopefully rule-out a theme-specific issue (theme functions can interfere like plugins).

I already tried to reset all plugings and theme (using twenty twelve) following this articel https://www.wpbeginner.com/wp-tutorials/how-to-fix-the-wordpress-white-screen-of-death/
No Luck

Now I’ve uploaded the original files again (without wp-content) and it’s running …

I checked all the file/dir rights and they where different then I have at another hosting provider. Changed it into 644 files / 755 dir.
Hope it will last now.

Excellent, I hope that lasts. ??

Unfortunately … not !
THe domain is now being moved to another hosting provider of which I know it will work !

Excellent, that’s probably for the best. ??