Dropping the Bowling Ball?

The problem usually is caused by the thumb hole size, weight of the bowling ball, or not drilled correctly. So the thumb hole is too big, then use bowling finger hole tape to make a snug fit, as mentioned in before. If not drilled correctly, the thumb hole may have to be filled and re-drilled. If too heavy a bowling ball, look for a lighter one for now, if you think you can use it in the future. Or, exchange your heavier bowling ball with someone who has a lighter one.
Remember, a custom bowling ball is customized for your style of bowling and hand features. Cheap, discount, and used bowling balls maybe a low cost, but after figuring bowling ball drilling, may not be that reasonable. Especially, during the off season between February-June, new bowling balls are discounted with free drilling at bowling alleys and pro shops. So it pays to compare, to get it done right, the first time.

Thumb Stuck in the Bowling Ball.

If it only happens once in a while, the bowling tip is use Easy Slide or some use Chap Stick on the back of your thumb. The bowling ball should slide off easier. Please don't use baby powder, it is illegal to use during a USBC game, because if drops on the floor or approach a bowler can slip and fall. Baby powder also leaves a residue in the thumb, that will build up over time. If the problem is more consistent, use sand paper or a small file to make the thumb hole bigger. But be careful, if you make it too big, then you will need to add bowling finger hole tape. This is a special tape that does not leave a gluey substance in the thumb hole. You would place the bowling finger hole tape at the back of the thumb hole for a snug fit. Usually, your thumb smells after a shower or a swim, and in the summer time heat and humidity. Hope this helps your Game, and your bowling enjoyment.