When there are beds on a moving structure, when the structure comes to a stop, the beds disappear - completely deleted, don't even drop as items.

If it helps, only tested with mechanical pistons and rope pulley, with the beds and blocks connected on a linear chassis.

Using Create 0.3e on 1.16.5, with OptiFine and JEI installed, on Forge 36.0.7

Happened to me too, the beds seem to disappear in any moving structure, not only pistons, and on every axis of movement.