No flow execution could be found with key 'e1s1'

[Y Levine]

Have a  Shibboleth3.3 service running --- couple of months now.

There seems to be increasing "No flow execution could be found with key
'e1s1'" type messages in the logs --- usually just the messages which we
assume user is hitting the back button -- today the message SQL error
message appeared below one of the messages.

Are they linked? What could be the root cause?

We are using Stoiragerecords --- on an Oracle DB

2017-08-23 17:35:11,486 - ERROR
[org.springframework.webflow.execution.repository.NoSuchFlowExecutionException:76]
- [118B81A145DA895C005F4C69E81E0C4E] - [IP Snipped] -
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.
    at
org.springframework.webflow.execution.repository.support.AbstractFlowExecutionRepository.getConversation(AbstractFlowExecutionRepository.java:172)
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(ConversationContainer.java:126)
2017-08-23 17:35:18,055 - ERROR
[org.springframework.webflow.execution.repository.NoSuchFlowExecutionException:76]
- [34DA7F97332EFAB4421B2D840CC080D6] - [IP Snipped] -
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.
    at
org.springframework.webflow.execution.repository.support.AbstractFlowExecutionRepository.getConversation(AbstractFlowExecutionRepository.java:172)
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(ConversationContainer.java:126)
2017-08-23 17:35:18,829 - ERROR
[org.springframework.webflow.execution.repository.NoSuchFlowExecutionException:76]
- [A835710D4AB00E298E6ED3B93A3091F2] - [IP Snipped] -
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.
    at
org.springframework.webflow.execution.repository.support.AbstractFlowExecutionRepository.getConversation(AbstractFlowExecutionRepository.java:172)
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(ConversationContainer.java:126)
2017-08-23 17:35:27,116 - WARN
[org.hibernate.engine.jdbc.spi.SqlExceptionHelper:144] - [] - [] - SQL
Error: 8177, SQLState: 72000
2017-08-23 17:35:27,117 - ERROR
[org.hibernate.engine.jdbc.spi.SqlExceptionHelper:146] - [] - [] -
ORA-08177: can't serialize access for this transaction

2017-08-23 17:35:27,118 - ERROR
[org.opensaml.storage.impl.JPAStorageService:755] - [] - [] - Error
deleting with expiration '1503534927112'
javax.persistence.PersistenceException:
org.hibernate.exception.GenericJDBCException: could not execute statement
    at
org.hibernate.jpa.spi.AbstractEntityManagerImpl.convert(AbstractEntityManagerImpl.java:1763)
Caused by: org.hibernate.exception.GenericJDBCException: could not execute
statement
    at
org.hibernate.exception.internal.StandardSQLExceptionConverter.convert(StandardSQLExceptionConverter.java:54)
Caused by: java.sql.SQLException: ORA-08177: can't serialize access for
this transaction

    at oracle.jdbc.driver.T4CTTIoer.processError(T4CTTIoer.java:445)
2017-08-23 17:35:27,120 - ERROR
[org.opensaml.storage.impl.JPAStorageService:853] - [] - [] - Error running
cleanup task for 1503534927112
java.io.IOException: javax.persistence.PersistenceException:
org.hibernate.exception.GenericJDBCException: could not execute statement
    at
org.opensaml.storage.impl.JPAStorageService.deleteImpl(JPAStorageService.java:763)
Caused by: javax.persistence.PersistenceException:
org.hibernate.exception.GenericJDBCException: could not execute statement
    at
org.hibernate.jpa.spi.AbstractEntityManagerImpl.convert(AbstractEntityManagerImpl.java:1763)
Caused by: org.hibernate.exception.GenericJDBCException: could not execute
statement
    at
org.hibernate.exception.internal.StandardSQLExceptionConverter.convert(StandardSQLExceptionConverter.java:54)
Caused by: java.sql.SQLException: ORA-08177: can't serialize access for
this transaction

    at oracle.jdbc.driver.T4CTTIoer.processError(T4CTTIoer.java:445)
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