Approvers using IE are not able to approve projects

ZD issue: https://gitlab.zendesk.com/agent/tickets/66159

The setup:

• GitLab 8.17.2
• Project requires 3 approvers
• Project has 6 approvers set

The result:

1 approver can always approve. Others, get an generic error message.

I attempted to debug this by manually recreating an approval as an affected user via the rails console and both merge_request.can_approve?(user) resulted in true, and I was able to apply the approval via the console. This leads me to believe this issue is something to do with the JS on the front end.

No relevant messages in the production.log.

Interesting tidbit: when we impersonated an affected user as the admin, we could approve as them via the UI.

@jschatz1 any ideas how we should debug this? I rarely debug frontend stuff, so I'm not even sure what we should be looking for or where?