your remark is very surprising because, as you rightly wrote, all the nouns finishing by the suffix -aine are feminine: I can add huitaine (one week), quinzaine (two weeks), neuvaine (a series of catholic prayers), douzaine (dozen) : all these are feminine. I’ve never read nor heard dizaine as a masculine noun, this is why I firmly believe that the two quotations you found must simply be typographic errors and nothing else.

I will add the same comment about your last quotation “plusieurs dizaine de milliers“: it should have been written “plusieurs dizaines“: there is absolutely no possible justification to that singular “dizaine“: it is a common noun, and common nouns always take a plural form when necessary: “plusieurs dizaine” can in no way be a valid exception.