We have a test client that sends messages as batches with SESSION_TRANSACTED mode. Each batch has around 10000 messages and there are 5 batches in one test iteration run. 
 
After sending 50000 messages, those messages will be consumed/removed from the broker. Then the test will be repeated with more iteration runs.
 
The test client always runs into CONNECTION_TIMEDOUT after some iteration runs with one of the following errors:
AMQ219014: Timed out after waiting 30000 ms for response when sending packet 43
AMQ219014: Timed out after waiting 30000 ms for response when sending packet 68
 
The problem was when the option "confirmationWindowSize" was set to 1MB, the client never recovered with subsequent reconnect and message send attempts. It just kept trying.