Time to time "JBO-25200: Application module is not connected to a database" exception is raised while browsing ADF application
Tune ADF application module by disabling "Support Dynamic JDBC Credentials".
However this solution may not work in your case, depends on the root cause.
If I understand this option correctly, it is needed only when application users must access DB using their personal credentials, but not one used for app in general. From my experience the latter approach is used usually (single DB user is created for app to access data). Thus this option is not necessary to be selected, especially when it involves additional lifecycles. And they make us problems like described above :)
Documantation about this application module option tell us:
Enables additional pooling lifecycle events to allow developer-written code to change the database credentials (username/password) each time a new user session begins to use the application module. This feature is enabled by default (true), however this setting is a necessary but not sufficient condition to implement the feature. The complete implementation requires additional developer-written code.
ADF version 188.8.131.52.0