Help!! For some reason when I freeze my frosting, after it is thawed out it has huge lumps of something in it. Feels like hard powdered sugar. My frosting is half butter and half shortening. Does anyone else have this happen, know why it happens or how to fix it once it is lumpy?

Welllllllll......sounds to me like you are not mixing the icing batch enough before freezing it.  Try this recipe:  https://www.cakecentral.com/recipe/22469/2-icing

Besides that you probably just need to re-whip it.  Have you tried that? Does that solve the problem?

Ditto what @kakeladi ‍ said.

It's so weird because I never ever have lumps in my frosting that has never been frozen. When I make it, it gets beaten 12-14 minutes. Is that not enough? The lumps only show up after it has been frozen. Refrigerated does not get lumps. And I sift all my sugar.

I will try your recipe too! Thank you! It is very similar to mine but the mixing method is different. And as we all know that can make a world of difference!