I have setup two custom snap areas. About once a day they stop working. When I move a window over the areas nothing happens. I have the UI only appear when you are over the area. Snapping to the window halfs still works fine, and everything else about BTT. To get the custom snapping areas back I have to quit BTT and relaunch it. Sometimes it will take a couple launches, but then it's good to go until a day or two later.
MacBook Pro 15" 2016
macOS Big Sur 11.2.3