see also:

• see also: https://forum.dokuwiki.org/d/17906-hogfather-update-leaves-a-white-screen
• go to your webserver's error log file (eg. CPanel's Error Log) and ascertain the issues, in my case it was a number of them:
  • Conf/local.php file error:
    • semicolon at end of a line referencing MS Internet Explorer: “msie=Microsoft Internet Explorer”';
    • invalid reference to Firefox in the StatDisplay plugin line: $conf['plugin']['statdisplay']['user_agent_keywords'] = '“firefox=Mozilla Firefox”
    • fixed by removing both lines
  • plugin fatal incompatibilities (all fixed by deleting these plugins):
    • cellbg
    • socialmark
      • PHP Fatal error: Declaration of syntax_plugin_socialmark::handle($match, $state, $pos, &$handler) must be compatible with dokuwiki\\Extension\\SyntaxPlugin::handle($match, $state, $pos, Doku_Handler $handler) in lib/plugins/socialmark/syntax.php on line 51\n
    • googlemaps
      • PHP Fatal error: Declaration of syntax_plugin_googlemaps_googlemap::handle($match, $state, $pos, &$handler) must be compatible with dokuwiki\\Extension\\SyntaxPlugin::handle($match, $state, $pos, Doku_Handler $handler) in /lib/plugins/googlemaps/syntax/googlemap.php on line 52\n
    • googleads
      • PHP Fatal error: Declaration of syntax_plugin_googleads::handle($match, $state, $pos, &$handler) must be compatible with dokuwiki\\Extension\\SyntaxPlugin::handle($match, $state, $pos, Doku_Handler $handler) in lib/plugins/googleads/syntax.php on line 45\n
    • flashplayer
      • PHP Fatal error: Declaration of syntax_plugin_flashplayer::handle($match, $state, $pos, &$handler) must be compatible with dokuwiki\\Extension\\SyntaxPlugin::handle($match, $state, $pos, Doku_Handler $handler) in /lib/plugins/flashplayer/syntax.php on line 51\n
  • plugin warnings only (do not cause issues at present but may do in future versions of PHP):
    • pagemove
    • displaywikipage