This issue is kinda like MCPE-119764
Are you playing with the caves & cliffs experiment enabled? if so, this is not a bug
This is intentional and not a bug
Every resistance effect level deducts 20% incoming damage, since Resistance 5 blocks 100& incoming damage, It is now invulnerable to damage except /kill command and void damage
This is an intended feature and not a bug because it spawns in the chest with a 1.5% chance
They do despawn since you have not interacted with them e.g. Tempting them. The Old Turtles were bred and they were tempted and fed by the player
The color of the sheep before it was renamed is what the wool the jeb_ sheep drops not a rainbow color
Pretty sure this works as intended, along with other non-full blocks such as slabs, stairs, walls, doors, etc.