- What's your servers hardware?
- What operating system runs on your server?
- What's your Redis version?
- What's your NGINX version?
- What's your NGINX config?
- What else is running on the server which might interfere with NodeBB / Redis (especially IO extensive tasks like backups)?
- Is your server using swap at all / a lot of swap during the times of lag?
- Have you tried running NodeBB in verbose mode?