It can be common for them to eat them. Stress, maturity, and other factors can take effect. They may eat them many times over before they get better. Once you get wrigglers I would typically pull the spawn so I have some future stock to work with and allow the pair to try and raise future spawns for following attempts. Some times I may only talk half a spawn and allow them to raise the other half. But some times they will eat them soon after messing/returning the cave. I also do not think dithers do anything helpful with apisto’s/rams at least not in my experience , at least from a breeding stand point. Other may have different opinions. But I’ve got angels that won’t spawn if they have other fish in the tank. I Remove the dithers and typically within 48 hours they’ll spawn. Useful tactic to get large spawns less often instead of getting smaller spawns every 10-14 days