Did you convert a polyline to the alignment?
If so, then if your polyline lines were not perfectly tangential to your curves then Civil 3D creates unconstrained lines and curves in the alignment when converting the polyline.
In the image below I converted 2 polylines. The top one was completely tangential and as a result you can see the grip for changing the curve radius. The bottom one I purposefully moved the line on the left to break tangency and you can see that the grip is not available to change the curve radius.
If you want to "fix" this you can edit the alignment geometry and change the curve type "Constrained on Both Sides (Free)". This will "fillet" the two lines and alter the curve to make it perfectly tangential. See images below.
Alignment before fix:
Alignment after fix: