Short feedback, I have disabled ufw and nginx and now messages are coming immediately like before (but no https).
So confirmed, the delay is a side effect of https/nginx config. I remember there was some comment on Chirpstack forum about API feed delay after enabling https? (can’t recall where it was exactly). Perhaps this is common for the front-end as well?
Restarted nginx service and now I see the lorawan frames immediately once uplink in sent from the node (before this change, messages were coming all at once with 5 min delay).
Perhaps it was due to proxy read/send timeout…not sure. Anyway, it looks ok now.