It seems to me the problem is clearly that the shared Hash isn't getting the DB handle

Yup. Just like I said. You can't share a DB handle, so you can't place it in a shared variable. On top of explaining this, I told you what you must do.

On a separate note you point on the DB handle is well taken. There won't actually be any concurrent DB handle access [...]

Apparently not, since I didn't talk about concurrency at all! So I didn't make whatever point you think I made about concurrency.