In that case check the PHP error log for errors and try to open the index.php?module=Proxy&action=getCoreJs file directly, to see if there is anything in it.
And to be safe, also check if there is disk space left on the server.
WARNING: /var/www/html/core/DataTable/Renderer/Console.php(152): Notice - Array to string conversion - Matomo 3.9.0 - Please report this message in the Matomo forums: https://forum.matomo.org (please do a search first as it might have been reported already)