PA-34 Flight Instructor reported during landing the aircraft started leaning to the right and the right main landing gear was retracting resulting in the propeller making contact with the ground.

Narrative

Incident Time: Approximately XG:10 local timeFlight Summary: We departed for a routine training flight in the designated practice area. All planned maneuvers were executed without any irregularities. Upon returning to ZZZ for a full-stop landing; we were instructed to join the left base for Runway XX.During the base leg; the tower provided a wind advisory for a departing helicopter; reporting winds 280° at 16 knots; gusting to 20 knots. (This information was verified post-flight). The crosswind component was approximately 10 knots; with a headwind of 17 knots.Approach and Landing:Pre-landing checklist: Completed approximately 3-4 miles from the airport.Landing gear status: Three green lights confirmed; no warning horn and visual confirmation on the convex mirror.Flaps setting: 25° (due to gusty conditions).Approach: Stable; smooth touchdown; no side loading.Landing Roll: Initially normal with all three wheels on the ground.Shortly after touchdown; while decelerating; I felt the aircraft leaning to the right. Initially; I attributed it to the wind; however; the right main landing gear was slowly retracting. Upon hearing the propeller make contact with the ground; I immediately cut the mixtures and secured both engines. Notably; the three green gear indicator lights remained illuminated even after the aircraft came to a complete stop.Aircraft History Prior to the Incident:XA:00: I conducted an earlier flight in the same aircraft with no abnormalities.XC:00: Another instructor flew the aircraft; no issues were reported.XE:30: I took the aircraft for a training flight; with the incident occurring at approximately XG:10 local time.