Can't trade with other players "player is busy"

When I try to trade with another player there is message "player is busy" displaying at the bottom left of the screen, and nothing else happens.

But only when I initiate the trade (when selling). When Buying, simply nothing happens. So I wait a few seconds and try to trade the seller, then the message shows up.

The only way I found to solve this is unparty/reparty the other player until the message "trade cancelled" shows up. Then clicking on trade displays the trade window normally, and the trade can proceed.

It's a bit annoying.

Note it started at the end of Blight, and I reinstalled my PC since then.

Edit: the exact message is "That player is currently busy."