Niels Peter Rasmussen

I might be having this problem, but it may be much worse on high resolution textures (Chroma Hills). It happens on windows but not on PS4 and is especially jarring on detailed textures such as rails and furnaces when viewed at a distance.

No amount of playing around in Nvidia Control panel has been able to fix it.

6k to 4k DSR has fixed the problem.

I don't think it's the same problem. I have found mobs (most of the time in my experience) reappear from portals used by the player and otherwise disappear. See MCPE-116572 which differs in a few details from present issue.

This problem is not equivalent to MCPE-66818

Only mobs going through the same portal as the player will spawn.

If the player goes through a portal far enough away that it's not a valid exit for the original portal, only mobs that have entered the same portal will spawn. It happens regardless of simulation distance and mobs either spawn in their entirety or not at all.

Sometimes mobs can spawn from a different portal than the player (expected behaviour), but I don't know how to make that happen consistently.

This also happens when crafting from inventory, so it's not unique to the crafting table.

I found a nether fortress today with one Blaze spawner. There was another blaze spawner room close by, but it was empty, roofed by netherrack like most of the fortress.

Perhaps related, in this world I found an End Stronghold that had no silverfish spawner, just stairs.

I had a rescued zombie librarian and traded her to level 3, only to have her disappear when I only just turned my back. She was almost right next to me. I broke a couple of bookshelves. Maybe that upset her.