Network requests from code (from WASM, at least, not sure about JS/HTML instruments) are impacted by MSFS server status. Due to the popularity of the 40th Anniversary update, the servers are under heavy load. I have just been disconnected as I type this. The Simbrief integration was tested heavily during the production phase. Until server loads lighten, the SimBrief uplink may be unreliable, this is unfortunately largely out of our hands.