If you utilize a custom spawn egg that typically summons a different entity type, it ceases to function properly following a world upgrade to a 1.20.5 snapshot, likely due to changes in the item storage system. For instance, if you acquire a spawn egg using the command:

give @p husk_spawn_egg{EntityTag:{id:"minecraft:llama",Glowing:1b}} 1

The husk spawn egg initially spawns a llama with the "Glowing" NBT tag set to 1. However, after the world upgrade, it will instead spawn husks rather than llamas. Nevertheless, other custom data from the spawn egg, such as the "Glowing" NBT tag in this scenario, remains intact.

Steps to Reproduce

1. Execute

   /give @p husk_spawn_egg{EntityTag:{id:"minecraft:llama",Glowing:1b}} 1

   in version 1.20.4.

1. Utilize the spawn egg to spawn glowing llamas as anticipated.
2. Upgrade to the latest snapshot.
3. Use the spawn egg again

Observed Results: The spawn egg no longer summons glowing llamas but rather glowing husks.

Expected Results: The item's data should convert to the new system, allowing the husk spawn egg to continue spawning llamas as intended.