If you import a character and attempt to trade, the game shades out the screen, leaving nothing interactable and no way to exit this state. I have read some comments stating that this may be unique to imported characters and also may lock when using the matrix.

Another issue that might be related is that there are certain tags that remain on the characters. For example; when I reopend the game and reloaded the save after experiencing the trading bug, the loading screen gave me the description for the epilogue.