To reproduce, on a superflat void world with no entities (no leashes or frames either), execute this command:

/scoreboard objectives add WolfAnger dummy

Adds the objective

After doing that command, spawn an untamed wolf then hit it in survival. When the wolf is attacking you, run this command:

/scoreboard players set @e[type=Wolf] WolfAnger 1 {Angry:1}

Sets the WolfAnger scores of angry wolves to 1. This should output this message:

Set the score of WolfAnger for player UUID to 1

but instead, fails then outputs this:

The dataTag does not match for UUID

I'm pretty sure I did the dataTags right. /summoning a wolf with the exact data tag makes it look angry, so it's just the command that's going bonkers.