403 on /messages/in_group/ with threaded=true

[jeffshieldsdev]

A week ago I started getting a 403 Forbidden error, trying to get threaded messages in a group.  I can get unthreaded messages, and threaded messages from another group.  I'm Admin of the group--and this worked a week ago.

Doesn't work:

• https://www.yammer.com/api/v1/messages/in_group/123.json?threaded=true 

Does work:

• https://www.yammer.com/api/v1/messages/in_group/123.json 
• https://www.yammer.com/api/v1/messages/in_group/123.json?threaded=false
• https://www.yammer.com/api/v1/messages/in_group/456.json?threaded=true 
  • Different groupId
• https://www.yammer.com/api/v1/messages/in_group/123.json?threaded=true&newer_than=1000000000000005 
  • adding newer_than = most recent messageId minus 1

Any thoughts on the cause or how I can escalate to Microsoft for troubleshooting? TIA.