I have also faced many crashes on realms that cause me to lose tons of progress in iOS v1.13.0. I had my game crash in the nether only to find out that I had been sent back thousands of blocks and had lost the loot that I had found even though there were other players still online. I also had an issue where I was the last person to log out of the realm and the next time I joined I had found out that I had lost hours of progress including blocks placed and items gained.
I play on iOS v1.13.0 and I had the same issue where a supercluster of different mobs spawned beside a forest close to my house. Other than this, mobs would usually spawn apart and not as fast.
I had my game softlock on realms while on the travelling to the overworld screen forcing me to restart Minecraft. When I logged back on, all of my items were gone as if I had died. They were not even on the ground anywhere, it was as if they were deleted from existence. This was on iOS 1.13.0