It appears you have a curved section of track leading into that switch, I had a similar situation with derails or splitting the switch. Resolved by adding a straight section before the switch. There were two other issues in my track system. One was when running conventional the switch didn't get enough current to fully throw.
The other was a mechanical issue where I found a plastic burr was in the switch mechanism. I opened the bottom of the switch, cleared the tiny obstruction and every thing has been fine ever since.
