If you are having AH issues, you can move your Cache, WTF, and Interface folders to your desktop or simply rename them if that doesn’t work disabling add-ons might also help.

You can install an Auction House add-on like Auctionator
You can try to unstuck from our website 

You can also try clearing your bags and moving the items to your main bag slots.
NOTE if you are trying to sell items that were transferred from BFA you can't.