Minecraft – How to remove a block itself near another specific block

It's due to unloading chunks

If you want to use commandblocks all over the map, you need to place them in the spawn chunk.

The spawnchunk is the area you spawn in (when not using a bed). This chunk is always loaded, so commandblocks will work even if there is no player near it

Unfortunately, you can only specify one spawn event.

From Commands/summon on the Minecraft Wiki (emphasis mine):

spawnEvent: string: basic_string

Must be either a single word (no spaces) or a quoted string.
Specifies the in-game event for the entity. Should be a spawn event (event name for entities in behavior pack).

This implies that mobs can only have one spawn event.