Hey Zachary,
this behaviour is unfortunately a current limitation on how the event handling (at least on windows) works.
UE won’t get any messages while a window is dragged and resized and our event loop will hang during that time.
Could you explain a bit more on the requirements for the data you’re sending?
For any realtime requirements you should avoid relying on the game thread, since it might also a hang in certain other situation like synchronously loading assets, level loading and similar.
A background thread or async task would be a good option in that case to make sure you’re network code or external connection is responsive regardless of the specific things happening on the game thread.
Kind Regards,
Sebastian