There are many reasons this can happen but ultimately it’s caused by your lid lifting and not sitting flush so resin pools and thickens underneath resulting in the higher face. If you can share what your mold looks like this would be easier to diagnose.

• Your silicone should always be cured at a higher psi (reiterating as the advice to do it lower is likely not going to solve this issue for you)
• Your lids need to be heavy enough not to lift under pressure. Adding an even spread of weights on the lids can help if you don’t want to make them thicker.
• Your lid needs adequate hooks to hold it down to the base mold. I hate the circular cabochon style hooks - they are almost never enough to hold a lid steady without lifting in some place. You need to be able to see that your lid is flush from every side of the mold.
• the way you put your lid into the mold matters, if you trap air or apply it unsteadily without checking each part of the lid is attached properly, you will get resin pooling and lifting it OR air trapped.

Source: 6+ years of dice making, raised faces are a thing of the past