In 1.14, shulker boxes no longer drop as a result of being broken by end platform regeneration as they did before. This is not restricted to just the end platform, other events that clear blocks, like generating the closed/opened exit end portal, regenerating obsidian pillars, etc also do not drop the shulker box.
In previous versions, shulker boxes had exceptions to always drop itself to prevent loss of their contents, including from explosions or other methods that normally destroy blocks without dropping, to be consistent with other containers like chests, which always drop their contents, no matter how they were broken.
This may be a result of the addition of loot tables for blocks, where the shulker box drop rules are now defined.
Steps to reproduce:
Open/create a 1.14+ world
Enter the end, place some shulker boxes, then exit
Re-enter the end
Observe that the shulker boxes were cleared and not dropped (whether or not they had contents is irrelevant)
Repeat these steps in a 1.11-1.13.2 world. Observe that the shulker boxes drop themselves on re-entry.
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Can confirm in 1.17-pre3.

Can confirm in 1.17.1 Pre-release 1.

Can confirm in 1.17.1.
Can confirm this behavior in 1.18 Pre-release 5. I've attached a video demonstrating this problem.
[media]Why exactly is this marked as related to MC-902, rather than duplicates? A bunch of other reports adressing exactly this did get resolved as duplicate...
@Dhranios MC-902 addresses the deletion of any block above the obsidian platform. This bug addresses the removal of a special feature shulker boxes had between versions 1.11-1.13.2 to always drop themselves, even when deleted, similar to how other containers always drop their contents even when deleted. This bug is not restricted to the obsidian platform, but any event that deletes blocks. This is most likely caused by the introduction of block loot tables in 1.14. Even if MC-902 is "solved", it probably won't affect the status of this bug because other block-deleting events exist.
Can confirm. Probably intended, so that players cannot suffocate when entering the end.