When i meant with sync it’s not about how the debris moves but on the actual fracturing. If i make a hole in a wall the hole can look a bit different on the client’s side. Not sure if it should be like that or not, so for an example if i want a building to fall by shooting down it’s support pillars on the server side the whole building might fall but on the client it doesn’t, I need to test some more tho because it might actually been a mistake on my side. I can take a screen shot later if it appears again. Thanks for the tip about the stretching, that was one of my problems too hehe 
About Large chunk override, i have been playing with it so i got the deal already but when putting it too high the debris just falls through the mesh also putting it too high will make the character ignore collision with the wall after being shot for an example, at least that happened to me. What i found out being the most visual and nicest option is to put the collision preset on custom for the mesh then check everything on Block execpt for Visibility, Worldstatic and World dynamic which i check on Ignore. I make so the debris despawn pretty fast also. Now there is no collision on the debris + they actually collide with the mesh before falling down giving some nice immersion.
Btw i found out one problem, dunno if it is because of the engine but i built a apartment which the walls was destructable, when i started the game the client’s game was pretty messed up, some of your bp destructable meshes was popping in and out being invisible and visible meanwhile everything else was good. Is it a limitation of the engine?