Zimy jsou studené a dlouhé tady - error? Why 'tu' and not 'tady'?
Tu and tady is the same, but the word order is awkward.
Although I can imagine it if you stress "tady" strongly. Still hard to imagine the context for such a sentence.
Can Duo say about wrong order in error message?
I think it can't.
Is zima not a word for cold?
It is, but it is a noun and it can be used in adverbial constructions. We need an adjective here, "studený" or "chladný" are both possible.