Both red sandstone and purpur slabs in the shulker box disappear after world conversion

There is a world conversion bug in the shulker box, which contains both red sandstone and purpur slabs. When I convert the world from Legacy Console Edition to Bedrock Edition, the shulker box with both red sandstone and purpur slabs inside disappear.

Steps to reproduce:

1. Go to Legacy Console Edition, click the play game button, and then click the create world button to start a new world from the play menu. Change the game mode to creative mode.

2. Obtain the shulker box and the red sandstone and purpur slabs from the creative inventory.

3. First, place the shulker box on the ground.

4. Then, click the shulker box and place both red sandstone and purpur slabs from the hotbar into the slots on the shulker box interface.

5. Finally, quit the shulker box interface.

6. Exit and save the world and exit the Legacy Console Edition.

7. Go to Bedrock Edition and click the settings button. After almost reaching the bottom, click the "storage” button. Then, click the “storage” button and scroll down until you see the old worlds option. Finally, click if you want to convert your old Legacy Console Edition world to Bedrock Edition.

8. Finally, click the converted world from the settings menu.

9. Check to see if both red sandstone and purpur slabs from inside of the shulker box disappear.

Observed result:

Both red sandstone and purpur slabs disappear from the shulker box.

Expected result:

The red sandstone and purpur slabs should not disappear from inside the shulker box.