I have been experiencing this problem for a long time, every time I endure it.
At some point I just get tired and write this here. I hope that Arma3 support is still alive.

Unfortunately, access to the inventory of killed opponents does not work stably.
Here is a video.

https://www.youtube.com/watch?v=WOAXANtxrQc

Sometimes the player needs to click many dozens of times to access the inventory of the killed. Sometimes it will require one click!
There is no way to reproduce this problem. There is only a negative random experience inside the game.

Please check why this is happening...