Hi. I have a same problem with Mattermost Team EditionVersion:2.0.0 Build Number:5950 and GitLab Community Edition 8.5.5 11f388a
It looks like this.
[2016/03/14
05:20:48 EDT] [EROR] /hooks/g3iu3rfdkinozf6z5xp13tq3hy:incomingWebhook
code=500 rid=7dfb1atgmiyp3n1o91oa8juxuo uid= ip=192.168.1.24 No text
specified [details: ]
[2016/03/14
05:22:54 EDT] [EROR] /hooks/g3iu3rfdkinozf6z5xp13tq3hy:incomingWebhook
code=500 rid=4u4cqdtsmtnkdfj995zanoymer uid= ip=192.168.1.24 No text
specified [details: ]
[2016/03/14
05:36:28 EDT] [EROR] /hooks/g3iu3rfdkinozf6z5xp13tq3hy:incomingWebhook
code=500 rid=xmhwo8qanjfdzbdoehuejd1mja uid= ip=192.168.1.24 No text
specified [details: ]
[2016/03/14
05:38:36 EDT] [EROR] /hooks/g3iu3rfdkinozf6z5xp13tq3hy:incomingWebhook
code=500 rid=uw31mahinigs8cywc75ut3op4y uid= ip=192.168.1.24 No text
specified [details: ]
[2016/03/14
05:48:20 EDT] [EROR] /hooks/g3iu3rfdkinozf6z5xp13tq3hy:incomingWebhook
code=500 rid=wxexy5x787fr3m4pq7gadti8ge uid= ip=192.168.1.24 No text
specified [details: ]
[2016/03/14
05:48:35 EDT] [EROR] /hooks/g3iu3rfdkinozf6z5xp13tq3hy:incomingWebhook
code=500 rid=uj9kt199jfgbpbomb4ok6ugauo uid= ip=192.168.1.24 No text
specified [details: ]
[2016/03/14
05:58:35 EDT] [EROR] /hooks/rfbfobaeujr6fcgnynz77itmpr:incomingWebhook
code=500 rid=8o74nkpucbnt8y8kdf18e35s1e uid= ip=192.168.1.24 No text
specified [details: ]