Successful rebase throws flash "Something went wrong. Please try again"

When using the "Rebase" action in the Merge Request widget, if it succeeds, a flash "Something went wrong. Please try again" will show up.

<namespace>/<project>/merge_requests/<iid>.json?serializer=basic response,

{
  "participants": [
    {
      "id": 1,
      "name": "Administrator",
      "username": "root",
      "state": "active",
      "avatar_url": "http://192.168.1.135:3010/uploads/-/system/user/avatar/1/avatar.png",
      "web_url": "http://192.168.1.135:3010/root"
    }
  ],
  "subscribed": true,
  "time_estimate": 0,
  "total_time_spent": 0,
  "human_time_estimate": null,
  "human_total_time_spent": null,
  "assignee_id": null,
  "merge_status": "can_be_merged", // sometimes "cannot_be_merged"
  "merge_error": null,
  "state": "opened",
  "source_branch_exists": true,
  "rebase_in_progress": false
}

The successful response includes merge_error: null which throws an error here, https://gitlab.com/gitlab-org/gitlab-ee/blob/8d717e9476e67ec6da59493ba9e76f74c1022c13/ee/app/assets/javascripts/vue_merge_request_widget/components/states/mr_widget_rebase.vue#L62

Even though the response included merge_status: "cannot_be_merged", refreshing the page gives a normal "Merge" option which makes me think it was actually successful.