Ahh, when he referenced his threads board i was thinking he had another threads forum that he also upgraded; my bad
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I have converted only one Classic board (with only 3 forums) to Threads. However, the new Threads board is on a new server, and is not live yet, so we can play with it until we get this problem worked out. The old Classic board is alive and running, on the "www." url, and the new Threads server is at the "www2." url.
Though I heard people whining about forums not redirecting before with the import map, so i was going off of that
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Just like Mark S wrote above. Perhaps they are encountered the same problem, but never worked through it.