I had the same problem. The first time, the adhesive strips held. Workaround: I cut a leftover cable duct (e.g. https://www.digitec.ch/de/s1/product/halemeier-kabelkanal-leuchtmittel-10851698) into an L and mounted it on the wall. The side wall of the L fits well under the Leafs. This way the cable duct carries the load (instead of the glue).