Hi Alistair.
You may start with these. Some of the articles/docs may require you to access using your customer/partner credentials.
Title : Avaya Communicator for Microsoft Lync: How to provide debug logs to support team for troubleshooting
Article ID : ADMN113002
Article Link :
https://support.avaya.com/kb/ext/ADMN113002
Title : Avaya Communicator for Microsoft Lync: Enabling debug logging when Avaya Communicator for Microsoft Lync is not starting
Article ID : ADMN112995
Article Link :
https://support.avaya.com/kb/ext/ADMN112995
PSN004849u
Avaya Communicator for Microsoft Lync 6.4.0.4 service pack is Released.
https://downloads.avaya.com/css/P8/documents/101029604
PSN004624u
Avaya Communicator for Microsoft Lync 6.4 (ACL) interoperability with Microsoft Skype for Business 2016
https://downloads.avaya.com/css/P8/documents/101015953
PSN004526u
Buffer overflow when deploying with large dialingRules.xml
https://downloads.avaya.com/css/P8/documents/101012080
Administering Avaya Communicator for Microsoft Lync on Avaya AuraŽ
Chapter 14: Troubleshooting Avaya Communicator for Microsoft Lync........................ 114
https://downloads.avaya.com/css/P8/documents/101010448
Arbi