Sounds like you lost contact with either the center rail or the outer rails. When you cleaned the rollers, did you clean the wheels as well? I assume this unit has at least one traction tire, which means that's one less wheel that will make electrical contact.
Does this engine have a tender? (I'm not overly familiar with modern trains) If so, the tender drawdar may act as an additional ground if the frame it is attached to is metal. If that could be the case, make sure that it is clean where the engine attaches to it and where it attaches to the tender's frame.
Is it safe to assume that other engines run fine through these switches, and that this engine did at one time work fine too? When is the last time the track was cleaned? If the engine runs fine on regular track (that may be dirty), it may not on a switch where there might only be a few of the wheels and possibly one one roller touching at a given moment.
Just a few ideas that don't cost much but time to try out. Hopefully it is something simple like dirty track.
Hope this helps,
J White