Exported in game using the addon, imported into the website to run a best in bags to help me clean out my bags to start into BfA, and it’s recommending my Off Hand Kingslayer be put into my main hand, even though it’s a singular item and can’t be manipulated that way. Additionally the item itself says off hand, and thus can’t be put into the main hand. Didn’t see any other bug reports about this, figured it’s lower priority due to being about legion artifacts, but figured I’d report it in-case any other off hand items get recommended into the main hand elsewhere.
If you include the addon export, from WoW, it can be looked at the way you see it.
I suspect this will be a artifacts are special snowflakes situation though, I think they’ve cause Yellowfive way more grief than he’d have liked.
Also, a temporary work around would be to “lock in” potential weapons and off-hands and optimize around that, or to put the artifact in your void storage, which is ignored in the current version of the add-on.