I reinstalled a Relational Data Store for a Base Enterprise 10.5.1 deployment and Portal does not appear to be able to find the registered Managed Database. When loading a Portal page, it attempts to query ArcGIS Server for a list of managed databases via the Portal proxy page (<webadapter>/sharing/proxy) but the proxy is giving an HTTP 500 error.
Trying to load the proxy page directly in a browse shows a 403 tomcat error page.
Stripping the proxy and attempting to query the ArcGIS Server REST endpoint directly returns the expected result
Looking for any suggestion on resolving this problem.