Loading a specific epic is extremely slow, participants fails

Loading &2697 shows a flash error with one of two values, intermittently:

One error is about participants failing, the other is notifications.

The right sidebar also takes a very long time to complete rendering. Two GraphQL requests take a long time to complete (>40s).

**The compound request for epic details:**

[{"operationName":"epicTodos","variables":{"fullPath":"gitlab-org","iid":"2697"},"query":"query epicTodos($fullPath: ID!, $iid: ID) {
  workspace: group(fullPath: $fullPath) {
    id
    issuable: epic(iid: $iid) {
      id
      currentUserTodos(state: pending) {
        nodes {
          id
        }
      }
    }
  }
}
"},{"operationName":"epicStartDate","variables":{"fullPath":"gitlab-org","iid":"2697"},"query":"query epicStartDate($fullPath: ID!, $iid: ID) {
  workspace: group(fullPath: $fullPath) {
    id
    issuable: epic(iid: $iid) {
      id
      startDate
      startDateIsFixed
      startDateFixed
      startDateFromMilestones
    }
  }
}
"},{"operationName":"epicDueDate","variables":{"fullPath":"gitlab-org","iid":"2697"},"query":"query epicDueDate($fullPath: ID!, $iid: ID) {
  workspace: group(fullPath: $fullPath) {
    id
    issuable: epic(iid: $iid) {
      id
      dueDate
      dueDateIsFixed
      dueDateFixed
      dueDateFromMilestones
    }
  }
}
"},{"operationName":"epicLabels","variables":{"iid":"2697","fullPath":"gitlab-org"},"query":"query epicLabels($fullPath: ID!, $iid: ID) {
  workspace: group(fullPath: $fullPath) {
    id
    issuable: epic(iid: $iid) {
      id
      labels {
        nodes {
          ...Label
        }
      }
    }
  }
}

fragment Label on Label {
  id
  title
  description
  color
  textColor
}
"},{"operationName":"epicConfidential","variables":{"fullPath":"gitlab-org","iid":"2697"},"query":"query epicConfidential($fullPath: ID!, $iid: ID) {
  workspace: group(fullPath: $fullPath) {
    id
    issuable: epic(iid: $iid) {
      id
      confidential
    }
  }
}
"},{"operationName":"epicAncestors","variables":{"fullPath":"gitlab-org","iid":"2697"},"query":"query epicAncestors($fullPath: ID!, $iid: ID) {
  workspace: group(fullPath: $fullPath) {
    id
    issuable: epic(iid: $iid) {
      id
      ancestors {
        nodes {
          id
          title
          state
          url: webUrl
        }
      }
    }
  }
}
"},{"operationName":"epicParticipants","variables":{"fullPath":"gitlab-org","iid":"2697"},"query":"query epicParticipants($fullPath: ID!, $iid: ID) {
  workspace: group(fullPath: $fullPath) {
    id
    issuable: epic(iid: $iid) {
      id
      participants {
        nodes {
          ...User
          ...UserAvailability
        }
      }
    }
  }
}

fragment User on User {
  id
  avatarUrl
  name
  username
  webUrl
}

fragment UserAvailability on User {
  status {
    availability
  }
}
"},{"operationName":"epicSubscribed","variables":{"fullPath":"gitlab-org","iid":"2697"},"query":"query epicSubscribed($fullPath: ID!, $iid: ID) {
  workspace: group(fullPath: $fullPath) {
    id
    emailsDisabled
    issuable: epic(iid: $iid) {
      id
      subscribed
    }
  }
}
"},{"operationName":"epicReference","variables":{"fullPath":"gitlab-org","iid":2697},"query":"query epicReference($fullPath: ID!, $iid: ID) {
  workspace: group(fullPath: $fullPath) {
    id
    issuable: epic(iid: $iid) {
      id
      reference(full: true)
    }
  }
}
"}]

**Another request which requests epic id and participants:**

{"query":"query epicDetails($fullPath: ID!, $iid: ID!) {
  group(fullPath: $fullPath) {
    id
    epic(iid: $iid) {
      id
      participants {
        edges {
          node {
            id
            name
            avatarUrl
            webUrl
          }
        }
      }
    }
  }
}
","variables":{"fullPath":"gitlab-org","iid":2697}}

This might be due to depth or the structure of the epic, however &1704 is deeper and broader and loads without error.