You may find that the following event fills up Windows Fabric event logs in Microsoft Skype for Business Server 2015 Director pools:
Log Name: Microsoft-Windows-WindowsFabric/Admin
Event ID: 16385
Task Category: Reliability
User: NETWORK SERVICE
Description: FM resolving failed with FABRIC_E_PARTITION_NOT_FOUND Event Xml
This issue occurs because the Windows Fabric cluster isn't set up properly in Skype for Business Server 2015 Director pools that have more than two servers.
To fix this issue, install the December 2017 cumulative update 6.0.9319.510 for Skype for Business Server 2015, Front End server and Edge server.