If you search the forum you'll find several threads regarding scikit-learn versions.
Essentially, you should be downloading the files from the Data Resources page, that matches the version of QIIME you are using. Note the drop-menu in the upper left of the page. If you are indeed using the correct version, then that means something altered your environment that changed the version of scikit-learn.
If you look through the first linked thread above you'll see an example of how to determine this by looking through the provenance.
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