I have created a part with screwholes (created them myself by using extruded cut and threads) and fillets in it. When I use the flex feature, the fillets (and part of the screwhole) become holes and I can look through the whole part. Did I do something wrong? How can I fix this?

I added an image of how it is supposed to look and an image of what happens when the flex feature is used.

I really need this to work!