Shoe/electric couplers or "thumbtack couplers?
Thumbtack indicates you have powered or created an electo magnet. Not too hard really; some kinda magnet field is present in any electrical connection. Maybe a short.
Shoe couplers indicate a wiring or an isolation issue. Maybe incompatibility, but Id think proper isolation of the cattle rails on a switch would do the trick.
Check isolation on the operation rails and center rail at the spot.
Inspect shoes for rub wear and loose/low contact nub.
