I have been running M+ Spires of Ascension a lot recently. My friends and I have been rotating the task of throwing the spear for Phase 2 (Devos in the Air).
Even though we are all experienced, a friend of mine tends to miss sometimes when he joins Oceania groups. Meanwhile, an Oceania friend of mine (who never missed Devos in Oceania) often misses with the spear when he plays with us in North America.
I think what’s happening is that latency can magnify the difference between where Devos is seen (on the WoW client) and where she actually is (on the server end). And Blizz might not have tested the Devos boss mechanism under significant latency.