If this problem is not caused by
Blue Iris crashing, then there are some other things you could try.
1) Open the Blue Iris web interface in a different browser that you don't normally use for anything else. There are lots of browsers to choose from... Chrome, Firefox, Opera, Edge, Internet Explorer, Safari, just to name the most popular ones.
2) You could try my UI2 page. It has two features which may benefit you.
2a) UI2 should automatically detect session loss and reconnect itself.
2b) UI2 has the unique ability to connect to other Blue Iris servers besides the one it is being hosted on, and when it does this, it does not rely on the session cookie of the remote server. So you could install the UI2 page on your reliable system, and use it to connect to your unreliable system and maybe, just maybe then it would remain reliable. You can set up additional servers for UI2 to connect to by clicking the system name in the upper left corner, then choosing
Manage Servers.
Keep in mind, all UI2 options including the server list here are stored in the browser's local storage, so don't expect to make a change and have it appear in other browsers or on other devices.
You can find the download link in my signature just below.