Found another cause though I can't reproduce as reliably: If I scroll the menu while hovered over a clue (no click), it will sometimes cause me to get locked. However, I think this may be a visual bug more than an action bug, as this lock also SOMETIMES allows me to grab already-placed clues and drag them (though they appear as the wrong color dot and check off a different, unmarked-clue which is why I think it's a visual bug. I think it is a misalignment from where the menu is vs. where the menu appears to be)