何かおかしそうなところがあれば教えてください。

checka-firestore.rules

service cloud.firestore {
  match /databases/{database}/documents {
    match /groups/{groupID} {
      allow get, update: if isAuthenticated() && isUserBelongingToThisGroup(groupID, request.auth.uid);

      match /users/{userID} {
        allow read: if isAuthenticated() && isUserBelongingToThisGroup(groupID, request.auth.uid);
      }

      match /boards/{boardID} {
        allow create: if (isAuthenticated()
          && isUserBelongingToThisGroup(groupID, request.auth.uid))
          && getBoardsCount(groupID) < 5;
        allow read, update: if isAuthenticated() && isUserBelongingToThisGroup(groupID, request.auth.uid);

        match /tasks/{taskID} {
          allow read, write: if isAuthenticated() && isUserBelongingToThisGroup(groupID, request.auth.uid);

          match /comments/{commentID} {
            allow read, write: if isAuthenticated() && isUserBelongingToThisGroup(groupID, request.auth.uid);
          }
        }
      }
    }

    match /users/{userID} {
      allow update, get: if isAuthenticated() && isUserAuthenticated(userID);

      match /groups/{groupID} {
        allow update, read: if isAuthenticated() && isUserAuthenticated(userID);
      }

      match /deviceTokens/{deviceTokenID} {
        allow create: if isAuthenticated() && isUserAuthenticated(userID);
      }

      match /opinions/{opinionID} {
        allow create: if isAuthenticated() && isUserAuthenticated(userID);
      }
    }

    function documentPath(paths) {
      return path([['databases', database, 'documents'].join('/'), paths.join('/')].join('/'));
    }

    function getData(path) {
      return get(path).data;
    }

    function getBoardsCount(groupID) {
      return getData(documentPath(['groups', groupID])).boardCount;
    }

    // firebaseの認証ユーザーかどうか
    function isAuthenticated() {
      return request.auth != null;
    }

    // Firebase認証がされているユーザーかどうか
    function isUserAuthenticated(userID) {
      return request.auth.uid == userID;
    }

    // グループに属しているユーザーかどうか
    function isUserBelongingToThisGroup(groupID, userID) {
      return exists(/databases/$(database)/documents/groups/$(groupID)/users/$(userID))
    }
  }
}