Thats physics for you.
The only real solution is to not use the landscape or increase the size of the landscape collision - or the fidelity of the simulation (sub step) - or both.
Additional possible fix:
Since they are BPs.
Trace downwards on the visibility channel (or probably just a box trace with sweep turned on).
When you hit, stop the simulation manually by switching simulate physics to off.
You can make the code for this pretty involved, like detecting if you hit a landscape actor and only stopping the simulation for the landscape actor.
What you aren’t going to do, is rely purely on physics. Especially if the simulation is server side and then synced…
You can barely get away with doing it client side and then synchronizing both server and other clients to it… and if the client is a slow PC you get issues even in that case…