Currently, issuing net.box requests from net.box on_connect trigger is not supported, because the trigger is executed synchronously by net.box connection's state machine, which sends/receives requests (i.e. calling e.g. conn:call from the trigger would block the state machine and stop any IO, including IO necessary to complete the conn:call).

It would be nice to remove this limitation, because there are users who want to define some global Lua functions on the server before sending any requests. Ideally it should be possible to issue requests from the on_connect trigger, and other requests should block (or fail if the trigger is called on reconnect) until the on_connect trigger completes.