Hello there @hibobiscool122, @Legerion, @0rca__, @ChronicleGaming, @Normallion5 and @J_WingBlade,
When switching from a newer version to a older version (for example 1.16 to 1.15), you need to reset your world (go to your file manager and delete the following folders "world", "world_nether" and "world_the_end".
If that doesn't help, please contact support here and click on "Contact Support" on the page linked.