Porcelain Crabs killing gobies?

I don't know if it's possible. Having a problem keeping firefish and small gobies alive in the small tank (10g). I don't think it's a water problem as I do regular changes of 20% once per week, levels seem fine, everything else lives fine including shrimp and corals. Problem is that after a few days I find that the fish no longer comes out or appears ill or just not well. I have 2 small porcelain crabs that seem to do nothing other than filter feed. I have never seen a porcelain crab get aggressive and they are afraid of almost everything, scurrying out of the way. They seem to completely leave anything else alone, even sleeping firefish in their caves. I think it's farfetched and there might be other explanations but has anyone really seen porcelain crabs go after fish that are larger than tiny?

Other livestock - 1 remaining Scarlett Red Hermit crab and a skunk cleaner. I doubt either of those two are responsible even more.