I have a rigify armature where the hip bones are locked in place. I'm trying to select all the bones and move them, and all of them do move, except for the very top hip bones. I made another rig from scratch and works perfectly but using rigify causes this problem.
Oh dear, I think there might have been a misunderstanding. When you add a Rigify Armature, what you get at first is only the Meta-Rig. Its purpose is to give you the possibility to fit the bones to your character in Edit Mode. You're not supposed to add constraints to it yet, and some edits to the armature are also unsupported. Once you're done editing the bones (and not deleting them), you'd generate the 'real' rig using an operator.
I've added a second Rigify Meta-Rig to illustrate that somewhere down the road, you might have accidentally edited the Meta-Rig in Edit Mode:
The armature on the left is yours, the one on the right a fresh rigify one. As you can see, there's relationship lines missing on your hip bones pointing to the spine. That's why the bones do not follow any longer the spine.
Retry creating a Rigify Armature, reposition the bones in Edit Mode to fit your character, and then locate the 'Generate' button in the Armature Tab of the Meta-Rig:
After you click it, you should get this:
This doesn't work on your Blend file any more, because some vital bones have been deleted unfortunately.
More details can be found for instance in this video https://www.youtube.com/watch?v=dYiAd_08-0k and many many other resources on the web on how to use it.