How to reproduce

1. Give yourself a named zombie head using

   /give @s zombie_head{display:{Name:"{\"text\":\"item\"}"}}

2. Place it down and break it
   → Observe that the name is lost, and it is again "zombie head"
3. Give yourself a named banner using

   /give @s white_banner{display:{Name:"{\"text\":\"item\"}"}}

4. Place it down and break it
   → Observe that the name is kept, and is still "item"