Errors Tracking Opens

We are having an issue with tracking opens for mailing. Click throughs track fine but opens do not. I inserted the URL for the tracking image into my browser and got a 500 error. I get the following in the PHP error log:

 [19-Feb-2020 16:37:18 UTC] PHP Fatal error:  Uncaught Exception: Function "is_admin()" is missing, even though WordPress is the user framework. in /home/mysite/public_html/wp-content/plugins/civicrm/civicrm/CRM/Utils/System/Base.php:264
Stack trace:
#0 /home/mysite/public_html/wp-content/plugins/civicrm/civicrm/CRM/Utils/System.php(203): CRM_Utils_System_Base->theme('<div id="crm-co...', false, false)
#1 /home/mysite/public_html/wp-content/plugins/civicrm/civicrm/CRM/Core/Error.php(196): CRM_Utils_System::theme('<div id="crm-co...')
#2 /home/mysite/public_html/wp-content/plugins/civicrm/civicrm/vendor/pear/pear-core-minimal/src/PEAR.php(922): CRM_Core_Error::handle(Object(DB_Error))
#3 /home/mysite/public_html/wp-content/plugins/civicrm/civicrm/packages/DB.php(998): PEAR_Error->__construct('DB Error: no su...', -19, 16, Array, 'INSERT INTO civ...')
#4 /home/mysite/public_html/wp-content/plugins/civicrm/civicrm/vendor/pear/pear-core-minimal/src/PEAR.php(575): DB_Error->__construct(-19, 16, Array, 'INSERT INTO civ...')
#5 /home/mysite/public_html/wp-content/plug in /home/mysite/public_html/wp-content/plugins/civicrm/civicrm/CRM/Utils/System/Base.php on line 264

We get the following in the CiviCRM log:

[error] $Fatal Error Details = Array
(
    [callback] => Array
        (
            [0] => CRM_Core_Error
            [1] => handle
        )

    [code] => -19
    [message] => DB Error: no such field
    [mode] => 16
    [debug_info] => INSERT INTO civicrm_mailing_event_opened (event_queue_id , time_stamp ) VALUES ( 34 ,  20200219164337 )  [nativecode=1054 ** Unknown column 'j.start_date' in 'where clause']
    [type] => DB_Error
    [user_info] => INSERT INTO civicrm_mailing_event_opened (event_queue_id , time_stamp ) VALUES ( 34 ,  20200219164337 )  [nativecode=1054 ** Unknown column 'j.start_date' in 'where clause']
    [to_string] => [db_error: message="DB Error: no such field" code=-19 mode=callback callback=CRM_Core_Error::handle prefix="" info="INSERT INTO civicrm_mailing_event_opened (event_queue_id , time_stamp ) VALUES ( 34 ,  20200219164337 )  [nativecode=1054 ** Unknown column 'j.start_date' in 'where clause']"]
)

Site is WordPress 5.3.2, CiviCRM 5.22.1