Kali Linux Persistence Not Saving Files on Root Partition

Hello, this is my first forum post here, so I'm sorry if I don't understand something, explain something badly or just am flat out wrong.

I installed kali linux on my USB by following the tutorial on official kali linux website and i tried following the tutorial here. after i successfully booted into my live usb with persistence first thing i tried is to update the system with apt-get update and apt-get upgrade and waited until it's finished. it downloaded some files and after a while i see that the upgrade has stopped with error "no space left on device", after i checked free space on root partition it said that there are 4 out of 8 gb left, it suprised me because i installed kali on 32 gb stick. after i tried rebooting i checked the available space was back at 8/8 gb free, and trying to update again i needed to download the same update files again to again have the same issue again. I don't know what is causing it, but it's getting pretty annoying that I don't have full device capacity available and that kali is not saving anything on root partition.

Again, sorry if this is just wrong, i missed something or my broken English makes it impossible to read.
Thanks for help in advance.