I'm loving the game and how much you interact with the community.
One thing that could help on the back-end is using WebSockets instead of polling for notifications. I noticed that the game makes some requests every 30 seconds or so, one of them being to check notifications. I've only implemented new connections in the system where I work, so I don't know how complicated the initial WebSocket setup is, but it's worthwhile in the long run. Instead of repeating requests, there will be a continuous connection between the front-end and the back-end, and the back-end only sends a message when there is actually a new notification. This could probably be used in other parts of the system as well.