Luke and Vader had several pre-ESB encounters in Legends and current canon, and while some very pretty dumb, some worked quite well. The new canon one I think managed to work around to quite well, and I think Chow and whoever is writing the new series is well aware of how “risky” this is so I’m not to worried about it. For all we know Vader might not even know its Obi-Wan, maybe he’ll be posing as someone else, or despite the dramatic “rematch of the century” statement it could be something that’s over quite quickly (i.e. Obi-Wan is forced to escape quite quickly or something ends up separating them). There’s a lot of ways this can go.

And lets not forget that SW continuity is already filled with minor continuity errors, strange coincidences and semi-retcons. Such as Ben telling Luke Yoda trained him (which is technically true), Ben not recognizing Artoo & Threepio in ANH, or Leia somehow remembering her mother despite Padmè dying in Ep. 3.