Dutch skills decay too quickly
Everyday I have to strengthen a 6-9 skills (out of 18 completed thus far). This seems like a disproportionate amount of time strengthening versus learning new skills. Often it is the same skill day after day after day ("present" seems to be a Duo favorite for repeated torture). Just today I strengthened "numbers" in the morning, and later in the day it was ungolden again. So frustrating. I am losing enthusiasm due to what seems to be a programming glitch.
I'm not sure it's a programming glitch. Duolingo uses a spaced repetition approach. It shows you things you've learned at times that will most help them stick in your head. If you keep the tree gold, you'll find it works really well. Sometimes that means you don't make any progress through the tree for a while - that's fine.
Duolingo takes account of how long it takes you to answer the question, and it takes account of whether or not you "peek" - whether or not you hold the mouse over a word to see what it means. When you can answer the questions quickly and without peeking, the skills will decay more slowly.
After you've strengthened the skills a few times, they'll start decaying more slowly, and then you'll be able to get further through the tree.
I have this problem with Danish too. One skill in particular, Adjectives 1, decays every day even though I finish it perfectly each day without e.g. hovering over words to check meanings. This doesn't arise with other skills so I'm sure it's a bug with this one skill.