I recently had this issue and could find no help for it and concequently spent about 2 days trying to fix it so I'm here to post a workaroundmethod that fixes it so you dont have to restart your game. So in order to fix your rock drakes not spawning in the volcano it's as simple as, installing the mod Simple Spawners by Darklore and plopping down a spawner in the volcano (Likely MUST be in the volcano because that's where their nest points are.) Once you do that you can adjust the size of the sawn field and at the side of the screen you should see multiple spawn options just simply find rock drakes. now if you're using a mod, fret not, this works for that too you simply must know the blueprint path for the modded rock drake, i.e. OmegaRock drake with DOX, the blueprint patch for that is, Blueprint'/Game/Mods/DinoOverhaulMODX/AlphaDINOS/RockDrake_Character_BP_OMEGA.RockDrake_Character_BP_OMEGA. I sure hope this helps anyone in the future fix their issues