Your idp-process.log and idp-warn.log may be filling with logs that are of little value and are just noise. This noise can be distracting for IdP admins and may cause concern as to its source and impact on your users (generally no impact). Using the logback.xml configuration you can drop unwanted noise logs before they are logged. 

From the Shibboleth wiki... Logging Configuration

"The biggest difficulty with noise in these logs relates to the very common occurrence of network connection issues that affect essentially any web server because of factors outside the software's control. These connection issues will typically result in a lot of extraneous ERROR content in both logs that eventually becomes fairly uninteresting to look at.

A second class of common issues is caused by clients that may timeout during the flow of a request because of user inactivity, leaving mid-transaction to go to lunch, etc. These will also eventually become noise.

Still another is the use of the back button.

You may eventually wish to apply filtering to the log events that are recorded, perhaps adding an additional appender to catch just those events and record them separately in the rare circumstance that you need the information."

The error logs below is cause by the user using the back button, a bookmark or similar. These can generally be ignored and even removed before they are logged. 

2017-10-20 18:47:13,175 - ERROR [org.springframework.webflow.execution.repository.NoSuchFlowExecutionException:76] -
org.springframework.webflow.execution.repository.NoSuchFlowExecutionException: No flow execution could be found with key 'e1s1' -- perhaps this executing flow has ended or expired? This could happen if your users are relying on browser history (typically via the back button) that references ended flows.
Caused by: org.springframework.webflow.conversation.NoSuchConversationException: No conversation could be found with id '1' -- perhaps this conversation has ended?
        at org.springframework.webflow.conversation.impl.ConversationContainer.getConversation(