Just today this issue began. While building a settlement I noticed I could no longer place certain items under the power category. Each settlement had a different item I couldn't place too which made it weirder. At Sanctuary it was all power pylons, at the Castle it was all conduits, and at starlight drive-in it was generators. And I know it isn't some cap on the number of items that can be placed because at Starlight Drive-In I had placed nothing at all there before this, but I still couldn't place any generators.

If anyone has had this issue and fixed it, or has suggestions please let me know.

I didn't have trouble with power items, but did have trouble with my defense items. It wouldn't let me place turrets. I thought I must have hit an item cap. I need to go back and check.