Note: tested with vanilla 1.15.2 server and client. In my testing, the bug occurred approximately 5 out of 25 times.

Steps to reproduce:

• Start a server
• Join the server with a player
• Pick up some item
• Open your inventory and pick up the item with your cursor
• While the player is holding the item with the cursor, close the server by using the /stop command in the server terminal
• Start the server again
• Join the server again with the same player
• The held item should drop on the ground as an item entity, but occasionally the item has disappeared