Channel unusable after attempted slash command use

See: http://forum.mattermost.org/t/one-channel-unusable-after-using-gitlab-slack-command/2961/3

Summary

After 8.17 upgrade, individual mattermost channels stop displaying messages after attempted slash command use.

Steps to reproduce

In 8.17:

  1. visit any channel (even DM)
  2. attempt to use a slash command (i.e. /<keyword> issue show #86)
  3. channel stops displaying new messages (perpetually displays "Loading...")

Expected behavior

Expect mattermost channels to display new messages.

Observed behavior

Affected mattermost channels do not display new messages, become unresponsive.

Possible fixes

Unknown