Check if
Blue Iris is actually the thing crashing. Look at the Log tab and see if it is really short and has a note about an unexpected shutdown near the bottom.
When UI3 detects session loss and reloads itself, that is not a crash, that is UI3 responding as gracefully as it knows how to after bad behavior from Blue Iris. It is on my todo list to improve the session recovery so it doesn't need to reload the page, but I have no ETA on that. My own BI systems are stable so improving how failures are handled is not so easy for me to do. lol.