Unofficial Skyrim Special Edition Patch

Built all three wings at Lakeview, in the order Bedrooms, Library, Storeroom. No achievement.

In the meantime, other achievements did appear, specifically Explorer.

By enabling the papyrus log, have the message:

[10/01/2020 - 01:32:01AM] Info: *Achievement 63 awarded - a winnar is you!*

Is that the correct number?

We don't have any way of knowing if 63 is the correct achievement for this or not, but since the log said it tried to award it, we know the conditions in the DLC are correct to do so at the very least.

The message in the log saying which achievement you just got is also embedded in the engine so we can't really look for that either.

Maybe someone who knows how to reverse engineer the code to look for this stuff can take a look at it and see what 63 is in SSE?

Achievement 63 does appear to refer to the Architect achievement. The proof for this is a line of code and a developer script comment that matches the description of the Architect achievement left in "BYOHHouseBuildingScript" on line 359/1320: "Game.AddAchievement(63) ; build 3 wings on a house".

Right, but does Steam actually see 63 as the achievement on its end? We know 63 is what the code is trying to give you in the game, but we don't know if that matches the list on Valve's end of the exchange.

This link for the Steam Database refers to the Architect achievement as "NEW_ACHIEVEMENT_63_0".

Well in that case this isn't a bug because the game issued the achievement as it's supposed to. We can't do anything about whether it shows up in Steam or not.