Yes, it's a good idea to see the Neurologist again, especially to make sure it's part of the same disorder, not a different condition. Obviously you'll need to wait and see what the test results show, as it sounds like your Neurologist is doing a thorough job to find the cause.
In the meantime, in the link below, scroll down to the "Episodic Ataxias" (7th from bottom). "Episodic Ataxia with Paroxysmal Choreoathetosis and Spasticity" (also known as Dystonia 9, or DYT9) is one of the "extrapyramidal disorders" you mentioned, and sounds similar to what you describe. Maybe the Neurologist will yet find this.
EA2 can sometimes also cause attacks which have Dystonia, see:
If either are confirmed, they can respond to the usual medications for EA (acetazolamide, and anti-convulsants to relieve muscle spasms Many of the metabolic disorders can respond to a special diet and supplements.).
I get Dystonia, including in the legs and feet as you describe, toes scrunching up, and feet can turn in at times. It comes and goes. For what it's worth, leg and foot dystonia isn't usually painful (unlike cramps), though spasticity can be painful. With Dystonia, the most pain I get is actually spasms in the neck and the headaches that come with it.
Dystonia can respond to "sensory trick, where -the spasm can sometimes be relieved if the affected area is touched or rubbed. So, the next time it happens, look to see if there's any spasms in his neck/back of head, back, hip or foot/leg, and try gently rubbing them, or the muscles just above or below the ones which are rigid. It might relieve the spasm and possibly any pain which might come with it. I find that, and laying down with a pillow supporting my neck in the right position can help relieve the pain.
Hope this helps.