Shulkerboxes/ Enderchests despawn in End

Hey, 

Im playing on the newest snaphot 20w17a and wanted to build an Enderman farm.

Placed shulkerboxes and Enderchest and they seem to just dissappear?!

First my shulkerboxes dissappeared when I left the End to get some stuff and then returned and then the same happened to my enderchest after that.

I tested it 2 times now and it happened again.

I recorded it on a video but cant upload it here cuz the file is too big.

Feel free to contact me for the video, if thats possible ( Im new to this forum thingy and dont know whats possible here + Im german, so my english might not be the best)