Closely relates to MC-189565 and possibly MC-199429

The bug

If a spawner is created which is set to spawn players,

Skipping Entity with id minecraft:player

will be continuously spammed to the game log while the spawner is in simulation distance.

How to reproduce

1. /setblock ~ ~ ~ minecraft:spawner{SpawnData:{entity:{id:"minecraft:player"}}}

2. Look at the game log

Expected results

The game log would not be continuously spammed with the same message.

Actual results

It is.

How to fix

Since player entities are a special case which shouldn't be treated like other entities in cases like this, it may be worth rejecting such a spawner entirely, converting it to a default spawner instead.

Compare the following spawn egg:

/give @s bat_spawn_egg{EntityTag:{id:"minecraft:playerror"}}

As the entity ID is invalid, it spawns a bat instead. Having invalid spawners converted to default spawners would make this more consistent and also avert this issue.