How do I fix in-game cc clothing spikes glitchi?

Hi. We need permission to be able to see the files.
Judging by description, you may have imported your blend into a package started from something that greatly differs from yours in shape.
For example, if you will import a dress (affected by skirt bones) instead of a swimsuit (no skirt, no skirt bones), there will be distortions in the skirt area.
If you will import long pants or a long dress (both affected by foot bones) into a swimsuit (does not go below ankles, no foot bones), the garments will distort in the feet area.

If you started the package from something that is similar to yours, it may just be a matter of lods. One or multiple lods (where the mesh spikes) are not affected by the right bones.

Basically we would need to see the blend and package files to give any specific answers