When upgrading an backpack through the storage request table, the contents of the backpack are lost.
Steps:

Versions:
Iron Backpacks 1.12.2-3.0.5-6
Simple Storage 1.12.2-1.2.4

1. Craft basic (leather) backpack
   2, Put any item into pack
   3, Upgrade pack to the iron tier through storage request table
   4, Open upgraded backpack and see inventory is missing

Thanks for your patience i couldnt get to these right away. I will investigate NBT fixes

https://minecraft.curseforge.com/projects/simple-storage-network/files/2573216