Note: SILVA only curates down to genus level. The species annotations are not curated, and a very large proportion are incorrect/inaccurate. So if you are using the SILVA database I would not trust the species level assignments, even if you are using full-length 16S (which in any case still cannot reliably distinguish some species so might not yield species-level classifications in that case). This is a feature of SILVA itself, not QIIME 2. See here for more details:
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