You might have a plugin that's failing. If you installed any custom plugins manually, they may not function correctly with this version of DokuWiki. You should look in they Grain Log for this grain to examine the errors from PHP-FPM. If the issue is in plugin code, you'll have to remove the plugin manually from the grain's filestructure via backup and restore. You can then try installing a new version of the plugin, or find a different one with better compatibility.
data/lib/dokiwiki/lib/plugins
folder and remove the
plugin's folder.