Galaxy S5 :: Deleting Trashed Emails From Trash Folder

I'm having a problem deleting all my trashed emails. Since I've gotten the S5 I've been getting rid of emails quickly. They also reside on my PC's Outlook so I decided not to have 875 emails cluttering up the S5. I use the combined view for my 2 non-Gmail accounts. All was working well until recently when there appeared to be 52 emails that remain even after I select all. 42 are from one account and the other 10 from the other account. I've tried deleting the trash from each account separately but the 52 keep reappearing when I "Show all folders" in the combined view (and the 42 from one and 10 from the other when I look at each account).

How can I delete this peskly "deck-of-cards" (52) emails? I guess the most drastic would be to delete the two accounts and start all over, but I'm curious to know how it might have happened in the first place.

Here's a picture of the situation. The only difference in the 3rd image is that after I delete, what shows as remaining in the trash is 52.