Bluetooth has limitations on it, there are first of all different levels of it, bluetooth 3,4 and 5, which have different data rates and speed, 3 has a range of up to 30 ft, 4 is like 200 feet and 5 is 800 (older versions of bluetooth were around 15'). Bluetooth also doesn't necessarily go through walls well, and can be blocked by metal and so forth.
I don't know what version of bluetooth Lionel is using (likely 3.0), but the quality of the bluetooth device you are using to control it also affects it, not to mention that potentially electrical noise from the layout room could potentially cause problems (I am not an EE, just mentioning this as a possible variable). Best service with bluetooth is going to be line of sight, and it degrades from there.
