よくある問題I started the Weekly Island expedition before the patch and then did one more and handed in after the patch was released. I did not get Essences.
The unlock requirements for this Essence are working as intended. One week's progression on Azerite for the Horde/Alliance is intended to be completed as a unit after the patch. Any progression from a previous week from before the launch of patch 8.2 will not award the Essence.