I hate to make declarations based on inadequate sample size, but I'm beginning to wonder if Frontier (despite their recent assurances to the community that they have a solid handle on their process and code management) may have broken HGEs again? I just spent over an hour flying to various war and civil war systems, and found a total of 3 HGEs in about a dozen systems (or more). ...of of those, NONE of them were the expected spawns (in Independent systems, a Civil War HGE spawned proto heat radiators, and a War HGE spawned proto radiolic alloys). The third HGE's timer was too short to explore. 
The HGE spawn rates WERE great before this last update...
The HGE spawn rates WERE great before this last update...