First off, I am sorry for your loss. It's never easy losing a frog, especially when there were no signs of it coming.

You keep mentioning water proof caulk from lowes, but never the brand. This is important. There are about 20 different caulks that lowes sells, of which only 1 or 2 are deemed safe for animal applications (not by the manufacturer, but from fellow hobbyists who have done the research). So, it is possible that you may have used the wrong type of caulk. Of course, you need to keep an open mind that this may not be the cause of the frog's death. It's easy to blame that, since it is the only new thing. But maybe some of the keepers of this species would notice something I would not, since I don't keep this species.