Missing Chunks and Lost Builds

I've been working on a world weeks. It's for me and my girlfriend's one year anniversary. I log off after working on some builds for a bit. I come back to chunks gone. They were loaded I was able to fly through them. As well as half of my builds gone. Things in chests gone. I don't know what happened. I did so much in that world and i was excited to show her what I was working on. i've got a couple weeks left still but I made so much progress. i tried refreshing the game but nothing

I was using texture packs and behavior packs and custom maps. could those be why?