If the fences are not in the blueprint state, then gates cannot be added to them. Furthermore, when you delete sections of the fence to create new blueprint state fence areas the area the just-deleted fence was is unbuildable, thus you cannot put a gate in. The solution is to build a jut-out fence and then place a gate there in that blueprint state fence.

The issue is the not able to build on just built ground, and then a quality of life piece added to this.

Is there a reason that this was marked as invalid? If I am doing something wrong it be great to know. Thank you.

Gates can be built on either blueprint or built fences, there was temporarily an issue where they faced the wrong way(since fixed) but actually placing them has not had issues.