Yes, I have read almost every report "similar" to the situation I'm in. I've tried almost every commented reply fix there was in those reports I read. (some I cannot because I don't understand coding...) But I have had no successful mob spawns. Natural Spawners alone are even worse. Only spawning 1-3 mobs every 10 mins or so.

I've been playing on Hard Mode for over a month now and maybe get 1 or 2 naturally spawned mobs (Zombies, Drowns, Skeletons. No Enderman, Silver Fish, Spiders, or Husks). It seems once the chunks have been loaded all natural spawning mobs just stop after a few in-game days. Even in caving systems. I don't even bother with torches anymore because mobs never spawn. The Phantoms don't seem to be affected at all. After the 3 days on Hard Mode; 5 or more spawn naturally. Each day I don't sleep more and more spawn. But I sleep to keep them away so other nightly mobs spawn (for mob farms). But lately I have to stay afk a lot longer then I want to just to get a few mobs to spawn so I can use the EXP to mend my tools. I've even built a guardian farm to gain more exp. When I first found the Sea Temple it was so hard to build the farm because of all the guardians that are there on Hard Mode. But I just finished the farm without any problem from any of the guardians because there was none. The funny thing was I didn't have any problem with the Elder Guardians because they had despawned. Even around the temple...there's no fish whatsoever. Not even Cod...

It's as if I'm playing on Peaceful Mode when I'm not.