This priest talent that gives shadow spells a 10% chance to stun the target for 3 seconds works but the little icon to show that the enemy player has been stunned by this talent does not appear.
I tested it again during the second test. It was a lag related issue (operating at 456 ms throughout the test) and the mechanic appears to be working correctly.
Don't forget that we ran the server in a "full-debug" configuration, allowing us to gather more data regarding crashes, but slowing down significantly the whole thing.