Probably caused by the fix of MC-132706 sticky pistons now do not update blocks they cannot pull. Slime blocks are apparently unaffected.
MC-138455 Sticky pistons failing to pull slime/honey blocks do not update blocks
MC-132706 Sticky pistons pull blocks that pop off
MC-132898 Multiple layers of falling gravity blocks break
MC-134555 Sticky piston does not update gravity blocks