Hi welcome to Fish Lore
I moved your question to a thread of it's own so it will get the attention it deserves.
I'm really sorry your little guys are disappearing.
They can squeeze through the tiniest areas so I would check outside the tank.
Are there any decorations they could have gotten stuck in? It would be a good idea to look inside the filter. It's possible they could have gotten up the out take.
I had one that got out of a tiny gap. I was lucky enough to see him hop on the rug. I was quite shocked he could get out.
I know fish will eat dead fish with nothing to be found. I don't know if that's the case with frogs, but they are carnivores.
Good luck.