Mattermost integration

Instance with Gitlab and Mattermost (omnibus installation) runs behind reverse proxy.
Integration works fine, and I get notifications in Mattermost on events in Gitlab.
But there is still one problem: from time to time I need to re-connect Mattermost with Gitlab by running /gitlab connect.
Could there be any timeouts related to websockets (on Gitlab/Mattermost side? on reverse proxy side?)?
What am I missing?

Thanks a lot for any help!

I used this app which is so good sharing of data is so easy and very fast we transfer to the other one. I suggest all of you once must use this app I hope you really satisfied.