20w45a, 20w51a, 21w07a, 21w10a
Steps to reproduce:
2. Place a repeating command block with the command:
3. Place a chain command block with the command:
4. Wait a little bit.
Notice that the fps decreases and the log gets filled with warnings about duplicate entity UUID's.
5. Look at the armor stand, and kill it using the kill command.
Notice that there is still a "targeted entity" entry in the f3 menu.
This bug did not occur in 1.16.4.