When using a character to steal in turn based mode, and having another character distract an NPC, may cause the UI to bug out.
In this incident, I used Astarion in turn based mode to steal from the Tiefling trader. There was an additional NPC who's vision cone prevented Astarion from sneaking away successfully, so I used Gale to distract said NPC. When Gale distracted the NPC, turn based mode ended and all UI options were obscured/removed. This was fixed by pressing "M" and fast travelling to a different location.