An exception occurred when trying to issue security token: The HTTP service located at http://localhost:32843/SecurityTokenServiceApplication/securitytoken.svc/actas is too busy.

There was an unexpected server reboot for our applications server and our service application features were failing. On checking, I noticed the below error in the Windows Event Viewer

Event ID: 8306

An exception occurred when trying to issue security token: The HTTP service located at http://localhost:32843/SecurityTokenServiceApplication/securitytoken.svc/actas is too busy.

On browsing to http://localhost:32843/SecurityTokenServiceApplication/securitytoken.svc ,  I got the below error

Fix

Identify the application pool for the Service Applications.

Application Pool -> Check Status -> Start