Minecarts, Boats and Armorstands don't have a NBT tag storing its item NBT. This results in the loss of any item NBT when placing and picking up these non living entities. Instead a similar approach to arrows, potions and tridents should be used where the entities store there respective item NBT.
Please provide the steps on how to reproduce and the observations and expectations. Please note that when making a report you have to include as much information as you can so that anyone reviewing the report can reproduce easily and understand the report.