Second GUI data erased upon chunk unloading

Hello! I am Esraja, and I'm new to modding. I currently have a block called the mass storage device. The purpose of this block is to store a bunch of items (hence the name). However, to do this, I need 2 GUIs to hold all of the slots (It stores 500+ itemstacks or is at least supposed to). I've already made a procedure to accomplish this, and it works perfectly until the chunk is unloaded. When the chunk unloads, the first GUI page is fine but the second is completely wiped. The same thing happens upon exiting the world. I can explain the way the procedure works if needed.

Thanks for your time,

                                      Esraja

P.S. - Unsure if this is the right section to be putting this in, so please let me know if I should post this in another forum section instead.

P.P.S. - I just remembered while proof reading this that the second GUI is linked to the first GUI through a button. The button opens up the next GUI which is identical (except for slot ID numbers) to the first. The block itself has the slot IDs of both GUIs (otherwise it crashes).