I'm having the similar issue currently in preview 1.18.20.24 (windows10)
When loading the game I see "Failed to load character 4"
Reloading any of my characters in the dressing room also fails.
Thankfully however, no characters had been overwritten when I returned the main release 1.18.10
Duplicate of MCPE-68978
Duplicate of MCPE-68978
Duplicate of MCPE-68978
This is especially noticeable / flickery whenever a lodestone compass does not have a lodestone assigned. It seems the enchantment glint animation resets whenever the needle moves, which in that case is constantly.
Update, I restored from a backup, travelled through the nether, did some villager trading, and returned to base via the nether again.
My cows, dog, and horses/donkeys/mules disappeared again.
Then I restored from another backup, did the same again but this time only 2 villager trades. On my return animals previously secured by leads were now roaming free (but the posts still appeared to have leads on)