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The general rule of thumb that once you buy an item for a quest it locks you out of other replay options. Well, all I did was click to see the rewards (didn't buy anything) on the 2017 Halloween quest and I got locked out of all the other replays. Tried logging out and logging back in, clearing my cache/cookies, restarting my browser, nothing. I'm trapped in the 2017 quest.
I saw that this was a problem on the French server as well. Hopefully they will fix it over here, too.