In some WordPress configurations, after upgrading from CiviCRM 5.11, the CiviCRM navigation menu bar has disappeared.
3 Answers
The problem only happens with certain configuration situations and seems to be related to changes in the asset caching system.
As a quick workaround, you can disable Asset Caching at:
/wp-admin/admin.php?page=CiviCRM&q=civicrm/admin/setting/debug&reset=1
Ok I figured out the issue after upgrading to version 5.20.2 (with WP 5.3.2).
If you read the migration document (https://docs.civicrm.org/sysadmin/en/latest/upgrade/wordpress/), it tells you to back up the civicrm.settings.php and restore it after the upgrade. If you do not do that, the civicrm Menu does not appear.
I was battling with this for some time now. Try changing the PHP version. For me 7.1 worked on IIS