How useful have players found this site?:
https://edgalaxy.net/hge
I'm sorry to say that I don't find this particular list useful. If you rely on that list instead of truly understanding how HGEs work, where they spawn and what they contain, it's no wonder you're frustrated.
Seems like it is often the case that the signals do not exist upon arrival.
Exactly my point. This list shows HGEs "after the fact" and teaches players to rely on a magic list that can't be accurate. It's not magic, really, and the in-game descriptions of the various G5 materials hint at how to find them. Granted, those descriptions could be better.
For example, one of easiest to find G5 manufactured materials are Core Dynamics Composites. You'll find them
always in Federal systems with a very high population and a state of none (i.e. no boom, civil war, outbreak, whatever). Enter the system, scan the nav beacon, enter supercruise, pick a HGE, and there they are! The other G5 materials need different preconditions to spawn. Use filters in the Galmap or Inara to find systems with these preconditions, and only look for
highly populated systems.
Now, I have to agree with you that the whole thing could be a bit more transparent and coherent. I don't know why Biotech Conductors and Exquisite Focus Crystals never appear at HGEs and if there are balancing or lore-wise reasons for it. That does seem odd, but then again, space oddities make the game what it is.