Creating a scoreboard with the "minecraft.killed:minecraft.player" on a realms server, then killing another player, you will not notice that the scoreboard is still not set.
Steps to reproduce:

1. Join a realm
2. Create the scoreboard with  /scoreboard objectives add testscore minecraft.killed:minecraft.player
3. Kill a player
4. Try to get the value of the scoreboard

Observed results:

Can't get value of testscore for <target>; none is set.

Expected results:

<target> has 1 [testscore]