This bad habit still occurs, not so much in stopping the air, but a way of providing compression.
I would suggest you keep visualizing your body as a balloon. Hold your breath and only let your lips hold back the air. Your cheeks may puff out, let them. Do not let the throat engage at all. Release the air keeping the throat relaxed. Try this several time releasing the air in short bursts, stopping it only with the lips.
Now do the same thing using only the tongue to release and stop the air.
Sing a note and stop singing only by disengaging the vocal cords, air should come out of your mouth without the vocal cords vibrating. Do this several times and then do the same singing exercise but close the mouth immediately after disengaging the voice. You should feel air pressure buildup in your mouth. Sing again and this time stop the air with the tongue. If you relax the tongue, air goes out and the throat is relaxed the whole time.
This was great advice, thank you. I also found that I had to open up and lower the back of my tongue, it was constricting the air supply. Now how to get this to stay that way as I ascend…