@hoang6 go in to your nodebb folder, the logs are inside the logs folder, open output.log and paste the last 20-30 lines which should show the crash.

@juan-g If I’m not wrong this is only for groups. Anybody can't make subforum both with his own group. This is interesting idea for plugin or like a feature for new version of core nodebb. Good for wide community forums on autopilot, when owner not have enough time to support all desires of members.