When I pack a double chest, then I place it down, half of the items pop out, and it acts like a single chest. When I break it, the chest on the right side stays.

Fabric 1.21.1

Version: 1.21.1-1.3.7.7.133

You will need to post this to the correct tracker for the Unofficial fabric version and Salandora should be able to take a look and fix.