Had the same problem with a new series 5.
I bundled a few of the solutions mentioned in this thread into one try and it worked (so one of them must have fixed the issue), I did this:
unpaired my old apple watch in my watch app
turned off bluetooth on my phone (so only wifi was connected)
clicked the (i) button on the watch pairing screen and set the language to English and the country to Afghanistan
AAsydney
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