I'm using WordPress 4.9.8 and I've upgraded our CiviCRM to 5.4.0. After that CiviRules 2.1 and CiviVolunteer 4.7.31-2.3.1 seem not working.
1. CiviRules 2.1, when click New rule, it backs to CiviCRM homepage
CiviRules> Find Rules> could find Rules but can not edit existed Rules. It only shows empty windows like this:
CiviRules> CiviRle Tags work ok
2. CiviVolunteer 4.7.31-2.3.1
Volunteers> New Volunteer Project: Go back to CiviCRM homepage
Volunteers> Manage Volunteer Project: Go back to CiviCRM homepage
Volunteers> Configure Roles> work ok
Volunteers> Configure Project Relationship work ok
Volunteers> Configure Volunteer Settings: Go back to CiviCRM homepage
Volunteers> Volunteer Interest Form: Go back to CiviCRM homepage
Volunteers> Search for... Go back to CiviCRM homepage
Please check and help to fix
Solution: I've follow Aidan's comment: Clearing the caches by go to Administer > System Settings > Cleanup Caches and Update Paths > Cleanup Caches And all works ok now