The bug
Saving your toolbar with a lodestone compass in it causes the lodestone compass in the saved toolbar menu not to update after the lodestone is broken.
How to reproduce
Connect a compass to a lodestone
Save your toolbar with the lodestone compass in it
Destroy the lodestone
Go to the saved toolbars tab in the creative inventory
→ ❌ Notice how the lodestone compass still points to where the lodestone used to be
This needs to be reopened. After the fix of MC-177136 I went back and tested this again in 20w16a, and it turns out that this is NOT a duplicate of MC-177136 and is a bug because lodestone compasses in your saved toobars do not update properly.