Manage out server keeps losing its ISATAP address

I have a DirectAccess environment, and have configured a group policy to enable an ISATAP address and add the ISATAP router to two servers. Both are 2012R2, fully patched, and are VMs on vSphere 6.x with vmnet3 adapters.

The one that's used most heavily is our deployment server (we use PDQ Deploy). However, this machine somehow loses its ISATAP configuration, seemingly at random. It doesn't appear to happen during a reboot - at least I've not been able to trigger it simply by rebooting it.

The problem has come to a head because we were trying to update some software for a computer in the field, and the manage out server running PDQ Deploy lost its ISATAP address in the middle of the operation during the night, leaving the user without the tools to do his job.

The only way I've been able to work around the problem is to open the Device Manager, select "Show Hidden Devices" from the View menu, then dive into the "Network adapters", delete the "Microsoft ISATAP Adapter", then reboot. This recreates the ISATAP adapter, and I can manage out again.

The problem seems to be associated with these two events - both 4202/iphlpsvc (since the first of the year, 28 of the 1st event, but only 1 of the 2nd - but ISATAP address isn't lost at every event log entry, it's happened perhaps 8 or so times since the first of the year):

   Log Name:      System
   Source:        Microsoft-Windows-Iphlpsvc
   Date:          6/8/2016 10:23:08 AM
   Event ID:      4202
   Task Category: None
   Level:         Error
   Keywords:     
   User:          SYSTEM
   Computer:      usUpdates01p.example.com
   Description:
   Unable to update the IP address on Isatap interface isatap.{0EF36F9E-C2E7-4D2E-8B9E-25C222FD0261}. Update Type: 1. Error Code: 0x490.

   Log Name:      System
   Source:        Microsoft-Windows-Iphlpsvc
   Date:          4/18/2016 4:54:16 PM
   Event ID:      4202
   Task Category: None
   Level:         Error
   Keywords:     
   User:          SYSTEM
   Computer:      usUpdates01p.example.com
   Description:
   Unable to update the IP address on Isatap interface isatap.{57D95105-3E6D-47C6-88D2-74F335109EA4}. Update Type: 0. Error Code: 0x57.

I've followed the advice in this article:

http://social.technet.microsoft.com/wiki/contents/articles/23982.event-id-4202-tcpip-network-interface-configuration.aspx

and have used netsh to reset winsock, but that doesn't solve the problem.

Does anyone have any idea what might be happening?

Kurt