Skills not turning gold after successfully completing the practice.
When a skills turns from Gold to the colored version and your strength bar goes down a notch. All you're supposed to do is practice said skill. After successfully completing a practice round. The strength bar should go up a notch and when it's full the icon should turn Gold again.
However, with some skills I find this not to be working. I'm currently learning Spanish. And Adect. 1 isn't turning Gold anymore for me.
The really sad part about all of this is that this bug has been a persistent bug for several months now (I believe it to be nearly a year now). This bug has been reported to Duolingo support several times, but to no avail.
I am a developer myself, and as a developer I really can't understand how a simple bug like this can persist for months while you do monthly updates.
I find the support for Duolingo to be pretty lacking.
The reason that the skill looses its gold status is that the mean value of all the word strengths for that skill falls below a certain level. Practicing a skill will normally raise that average above the level and make it gold again but this is not guaranteed. You may need to practice 2 or 3 times (occasionally even more).
It could still be technically possible with with two complex and opposing algorithms for this to happen. Unfortunately it could be possible that the practice does not select any of the weak words so it would average would not change, although i have had to practice numerous times myself on occasions, 12 times does seem excessive but still technically possible.
We used to be able to see strength of individual words until the feature was removed. Now some users have a words tab but i do not know if this gives the same information as i do not have it myself.
You could always try re-doing all the lessons as that should turn it gold again.
I know this is a really old thread, but I started having the same problem (with German "idoms") - apparently, either duolingo adds words to existing lessons, but then doesn't include them in the "strengthen" option, or it loses track of the fact that you've learned the words at all, so it decides it can't give you gold. If you go back through the individual lessons for the topic that won't turn gold (instead of just continuing to "strengthen"), it should unstick, and turn gold (at least, it did for me!)