Hi there,
Over the weekend, we upgraded ArcGIS Enterprise from version 10.81 to version 10.91. Numerous custom WebApplications had broken down during the upgrade. Webapps gave an error message at startup: Cannot read properties of undefined (reading 'version').
Fortunately, we found this discussion, based on which we understood to fix web applications by manually editing them with the excellent ArcGIS Assistant tool developed by Esri. Now all webapps are running nicely on the Enterprise Portal again.