My progress on my lessons keeps backtracking on a daily basis so I'm going over and over the same lessons even after I'm mastering the lesson daily.....
I suggest you use the "strengthen" feature on a regular basis. Since you're at Level 9, you may want to go back and strengthen all the modules. Then go on, but keep strengthening as you go. You'll still lose the gold from time to time, but it won't be so annoying to get it back.
I'm sending you two lingots to smooth the aggravation