Is this trying to open the admin pages? If not, open the dashboard, add the cache widget and then clear cache. Also clear browser cache.
Then navigate to the page again. Sometimes the page requires one attempt to trigger execution of that php and a second time will render the results of the code.
After numerous errors, the site suddenly started working. I don’t recall doing anything except accessing the site again or accessing the page again. Sometimes I had to delete the extension or the theme and select the option to delete the data. Then activate it again or reinstall the extension or theme. Then accessing those pages seemed to work just fine.