4.0 client failed to send message, but other users saw the message being sent

Summary

Failed to send message but other saw the message sent and reopen the client will show the message successfully sent

Client version

• 4.0.4(539) (Mac)
• 4.0.1626 (Windows)

Environment

• OSX 10.10.5
• Windows 7
• Windows 8
• Windows 10
• Web client (some user say it happen on web client too)

Step to reproduce

1. Send a message in room
2. Message will keep loading and say failed to sent
   

Expected Results

Message is successfully sent

Actual Results

Failed to sent the message and have to reopen client

Workaround

1. Use web client at https://www.hipchat.com if user don't have any issue with web client
2. Close and reopen HipChat client