The Bug
The heavy core has no required tool to break it with
Reproduce
Get a Heavy Core
Place it
Get a Netherite Pickaxe
Mine it with your hand
Mine it with the Netherite Pickaxe
Observed Result
They had the same breaking time
Expected Result
It would mine faster with a tool
Note
This is because the core is not assigned to any mining tool tag
On Bedrock, the pickaxe mines it faster.