I had posted earlier about the Riven King's Throne not being sittable. So I decided to do some more research and give some more details. I am in Boldertree Refuge and trying the place the throne in the first open-room space.
After some fiddling around with it, I believe I have a cause. I took the throne and placed it back in my inventory. Then I went to place the item, but I did not do anything other than move the mouse around until the throne glowed green. No push / pull, or anything else. And I was able to place their throne and sit in it. It was not where I wanted, but it was working.
Then I picked it back up again and put it back in inventory. I again tried to place the throne. Using the above trick I got it to where it glows green. Then I used the push / pull feature without moving the chair anywhere. I would go one "tick" up (pull) and then immediately go one "tick" back down (push) to the original position. Then I would do one "tick" down, then back up to the original position. I found that about 2/3 of the time, it broke the chair and it was no longer usable (stayed glowing yellow). So push/pull was messing it up somehow.
I then decided to test another element. I tried to use the in-game align. Again, using the trick above, I was able to wiggle the mouse until the throne glowed green. I then moved the throne to where I wanted it, and pressed the align button. It glowed yellow, and nothing I did would make it glow green again.
So, I decided to take the throne to another house (Sugar Bowl Suite). There the throne was able to align properly using the align function and was fully usable.
I took the throne to the Flaming Nix Deluxe Garret. Tried to place the throne, and could not place it where it was usable. I was able to use my trick of placing the item from inventory by just wiggling the mouse around until it finally glowed green. But again the push / pull would make it unusable even if you push one tick and then immediately pulled it back one tick. Align would not work either. It made the chair glow yellow, and I could not arrange it in any way that would make it usable. I placed it back in inventory, then was able to use my mouse wiggle trick to make it glow green again. Then moved the throne to where I wanted it and pressed align. It stayed glowing yellow and was unusable.
To be thorough, I next took the throne to Autumn's-Gate. I was able to place the chair using the align button and it worked properly.
My tentative conclusion:
1. In certain houses, the align feature does not work properly for chairs. I can repeatedly trigger this error at will in the Boldertree Refuge and Flaming Nix Deluxe Garret. Every time.
2. In other houses the align feature works as expected.
3. Is it possible that the texturing of the floor is messing up the align feature? Smooth-floored places such as the Sugar Bowl Suite work fine. Rougher texture floor (stone and brick) found in the two houses that I can repeatedly cause the error suggests the interaction between the flooring and the align feature may be the issue.
4. Yes I did turn off addons and only used the in-game features.
5. This has been tested over the span of multiple logins, so reloading ui will not fix the issue.
6. This has been tested with multiple characters. Consistent results regardless of character.
7. I tried other chairs / seats / thrones besides just the Riven King's Throne. The problem was consistent regardless of type of chair.