Translation:How many centimeters of wool are left?
Wool is countable? Really? Do you say, "I'm buying two wools today"? That sounds strange.
In American usage, at least, wool is uncountable, since it's measured by volume or weight. Unless you're talking about woolen yarn (usually called just "yarn"), which is countable in terms of balls or packages.
Here it doesn't matter one bit if wool is countable or not. The verb agrees with the subject which is centimeters, not wool. Wool is the object of the preposition of, and does not affect the verb form.
But wool is actually uncountable. The way way an uncountable noun becomes countable is my specifing a unit, or having it implied. A coffee generally implies a cup of coffee, a water most often a bottle of water, but something like a beer changes from bottle/can to glass depending on where you are. Wool is measured by centimeters in metric systems or still by feet or yards in the US. It has no default unit however. One wool isn't understandable at least to most people, although theoretically it could mean something in some industry or other.
The idea of measuring wool by length may seem strange, but for purposes of spinning, wool is commonly formed into a "roving" that is measured in length (i.e. centimeters). So I think of this sentence as question being asked by someone who spins wool into yarn as a hobby.
For those who are wondering, filato is the Italian word for "yarn."
I have found the speaking exercises to be quite buggy in all the languages I do on Duo. One problem, however, is that they are very affected by your device, your internet connection, and the internet in general. It can often be essentially like a bad phone connection. I mostly have them turned off in settings, although my last update changed that and I haven't changed if back yet. If you remember to read the exercises out loud any way, you won't miss anything. If you are particularly worried or interested in your pronunciation/accent, recording yourself reading a short passage will give you a better way to judge. And if you're actively learning and speaking, repeating the process every couple of months will give you a good sense of your own improvement.
It's not that Duo has changed and no longer shows typos. The problem is the algorithm the computer uses attempts to identify typos based on a extrapolation of "rules" of how people make typos so it can distinguish between a typo and a word. Some typos inevitably don't fit those rules, so they are missed. Writing the rules is quite difficult in the best case, but Duo has two different languages to take into account, so they have a particularly difficult job. You, on the other hand, aren't a computer and should be better able to identify your own typos if you simply take the time to check.
It's not a malfunction as much as an omission. Each exercise has a unique database which includes every variation that is an accepted answer for that particular exercise. Even the simplest exercise is going to have quite a few variations and it's quite common to have over 100 and a few have variations in the thousands. With all the nuances they have to consider, it's not surprising that they miss options, even fairly obvious ones because they concentrate on the less obvious ones. But that's why it's important for you to report any answer that should have been accepted, except if there is another error in the answer. It definitely can be frustrating, but it's not surprising.