The high packet loss is the main issue; it invalidates your data and connection is closed.
That’s why is important to form a nice pack of data (struct) and send it at once, causes much less overhead than sending individual properties. This is not just for UE games btw;
I think UE4 packs properties that it replicates by default, but in your game logic you may be sending too many single values from lots of classes and making the net driver going nuts.