Chunks were deleted

So i was playing on this one world on Bedrock on my phone, occasionally, I played with friends. This morning playing on the world was fine I was making significant progress to beating the game until I logged in this afternoon, I realized I was falling through the world, I hoped it was just a loading error, but after dying to the void and checking out my base I realized that chunks of my base was turned into void and other chunks had just been completely regenerated after being played on for the majority of those 900 days, I did not know this was possible so I never backed up my world. It feels like there is nothing I can do and I have wasted many hours on nothing. The 3 pictures show the aftermath, and the last one is a pretty recent photo of the map of my island.