It sounds like the tips you are using are coming into contact with an agent that breaks down the plastic. It may be that you’re getting the bonding agent that adheres the gel to the natural nail on the tip.
If it’s not that, it could be the cleanser you use before you apply the products. Many gel cleansers contain acetone and acetone will break down the tip, causing cracks. It is common for the cracks to show up later. The other thing that could possibly be happening (this is the least likely) is you are cleansing under the nail with an acetone-based product. — Amy Becker is founder of Masterworks Innovations.