I had this problem too in an old local world upgraded to the experimental version.
I solved it by moving the DataPack "update_1_21" to the bottom of the list in the level.dat.
This works:
level.dat
+- DataPacks
+- Enabled
+- vanilla
+- update_1_21
Experimental blocks don't drop their item when in this order:
level.dat
+- DataPacks
+- Enabled
+- update_1_21
+- vanilla
I had this problem too in an old local world upgraded to the experimental version.
I solved it by moving the DataPack "update_1_21" to the bottom of the list in the level.dat.
This works:
Experimental blocks don't drop their item when in this order: