In our DocuSign Demo environment, we noticed that when several envelopes were voided, we did not receive the corresponding connect events. We checked the connect logs and the envelope ID's are not listed. We checked the envelopes in DocuSign and verified that the envelopes were properly voided. We sent a couple more through and recieved the events successfully.
Has anyone else experienced this issue and if so, were you able to correct it?
I'd suggest you verify the following Connect settings via the DocuSign UI (Preferences >> Connect >> [Connect_Configuration_Name]).
Ensure that Allow Envelope Publish is selected: 
Ensure that Envelope Voided is selected, and also that All Users Integrated is selected (assuming you want Connect to send notifications for all envelope void events, i.e., for all Envelope Senders) 
Provided that the Connect configuration settings are specified as described above (and logs are enabled via the Enable Log checkbox), you should at least see the Envelope Id in the Connect Log file anytime an envelope is Voided (even if some connectivity issue prevented the message from actually reaching your listener). Also, keep in mind that the Log file only preserves the 100 most recent log file entries -- so if there have been more than 100 messages sent since the Envelope Void that you're looking for in the Connect log, it's expected that you wouldn't see that Envelope Id in the log file.
Working with enterprise support, we determined that our missing connect event problem was caused by using the 'Send on Behalf Of' feature. We were listing the authenticating user in the 'Select Users to Integrate', and needed to list the send on behalf of user.
Also, Require Acknowledgement is NOT mentioned here and can and generally does play into debugging connect issues.
Related article: Docusign Connect retry frequency when require acknowledgement enabled
