This doesn't sound normal to me... but the one thing I will say is this.
I've only ever had to adjust my Zon necks once after I settled on string gauge and brand, etc, but the process of adjustment took a few weeks.
In my experience, once you turn the truss rod, it takes a good week or so for the neck to settle in to that adjustment... and it doesn't take much of a turn to get the neck where you want it either. It's not like wood where you get the response immediately.
Because of this, I could see how a person might over-adjust because they're expecting an immediate change and it might seem like your neck is moving a lot, when in reality, it's just settling in to the adjustment you made a week ago.
Give your neck a few weeks to completely settle in... Figure out where you want it and give the truss rod a 1/4 turn. Give it a week to settle, and then do the same. It'll take some patience at first, but once you get it where you want it, there shouldn't usually be much movement at all.
Again, this is my experience... But try it out and see what happens.