We have received reports that after upgrading to v1.16.0, the amount of websocket connections is very high relative to pre-upgrade

This is due to older socket.io clients (running on version 2) attempting to connect to the new socket.io 3. These protocols are incompatible, and so the connection is rejected, and NodeBB was configured to try indefinitely.

This is ok. Over time, as your users close their browser windows (or refresh), they will automatically start using the latest version, and socket usage will return to normal levels.

If you are worried about the excessive traffic, you can configure a nginx condition to drop requests with the query string ?EIO=3. Please see the issue linked above for more information.