Depends on what you are doing but its probably a media bug which is used for various things to interact with the media

From: freeswitch-users-bounces@lists.freeswitch.org [mailto:freeswitch-users-bounces@lists.freeswitch.org] On Behalf Of Naveen Tamanam
Sent: Thursday, September 29, 2016 3:31 PM
To: FreeSWITCH Users Help <freeswitch-users@lists.freeswitch.org>
Subject: [Freeswitch-users] What is the meaning of Attaching BUG to sofia/external/number

Hi,

Often I see the message like "Attaching BUG"  in freeswitch console logs.

What is the meaning of "Attaching BUG"

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Thanks & Regards,
Naveen Tamanam