Pistons can force shulker boxes to pass through solid blocks when activated shorter than 1 tick, for example when the piston activate by observers.
This issue related to MCPE-46746 (which fixed), but this new problem happens only with shulker boxes, and only when the pistons activate in that specific short time. - so you can reopen MCPE-46746 or leave it as a separate ticket.
See picture and watch the video to understand clearly the problem.
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Tal, as I explained on MCPE-46746, it's the next shulker box being placed, and not the piston, that forces the shulker box item entity to pass through the full/solid blocks. So what you have described cannot be reproduced.
My guess is that what you expect to happen in the build in your picture, is that all of the shulker boxes would be collected by the hopper underneath. The actual reason that all of the shulker boxes are not collected is that (a) hoppers do not collect item entities from the entire block space above them (MCPE-55824), and (b) the next shulker box is placed before the broken one falls into range of the hopper. Notice that if you slow down the circuit then all of the shulker boxes get collected.
I do think that you've found a significant issue here, so I will update MCPE-55824 when I have some time.

Tal, as I explained on MCPE-46746, it's the next shulker box being placed, and not the piston, that forces the shulker box item entity to pass through the full/solid blocks. So what you have described cannot be reproduced.
My guess is that what you expect to happen in the build in your picture, is that all of the shulker boxes would be collected by the hopper underneath. The actual reason that all of the shulker boxes are not collected is that (a) hoppers do not collect item entities from the entire block space above them (MCPE-55824), and (b) the next shulker box is placed before the broken one falls into range of the hopper. Notice that if you slow down the circuit then all of the shulker boxes get collected.
I do think that you've found a significant issue here, so I will update MCPE-55824 when I have some time.