Chunks getting deleted in my old world on newer version 1.21.50

I was just playing Minecraft pocket on 1.21.44 everything was going well but after 2 days of playing Minecraft my game automatically updated to 1.21.50 and when I opened my old world all the chunks around me were getting deleted 😔 don't know why I thought it's maybe some problem while exporting I reinstated the world and more chunks got deleted this time I'm getting frustrated after this plz 🙏 mojang plz 🙏 fix this issue or I may lose my 3 years old world plz