Wheels keep going untrue

As the title says, my wheels untrue itself, my lbs checked and balanced the tension last time we trued it.
But it kept going untrue.

It's tiagra 4600 laced to archetype with double butted ACI spokes.
The rims is not bent.

So what seems causing this?

Don't take this the wrong way, but...

• How any spokes does each wheel have?
  
• How heavy are you?
  

None taken.
78-79kg right now
Both are 32H

Supposedly still within limit no?

I'd say so. Is it one wheel, or both? Front or rear?

Outstandingly both!
Spokes and hubs are new, the rims are secondhand but we (me and the mech) can't see any fault.
Can it be the spokes though?

ACI spokes are ok , have built up several sets of wheels with them, with no problems would be very difficult to tell what the problem is without seeing them, could be over tension, under tension,
bad build technique , extreme rider abuse who knows?

Hmm so there are the possibility of under/over tension? Even if the tension is balanced?
So maybe it is this or wheel built error.

I'm pretty sure there's no abuse (at least no extreme) my previous bike is a stock bianchi pista with pretty much the same riding style :) and the wheels are still true

A process of elimination might suggest that it could be a problems with the nipples.
I had a similar problem where my local LBS mechanic reckoned the spokes were causing the nipples to split thus causing the wheel to be out of true!
Worth thinking about?

A poor rim can be trued but have unevenly tensioned spokes. These can then loosen when used.

How was the previous wheelset unlaced? If the spokes were just cut this can stress and mess up the rim.

Split nipples , may be possible with alloy ones with some serious over tension, and or over long spokes.

Also

Did your mechanic stress relieve the spokes?

If this is a persistent problem it sounds like twisted spokes and/or not enough tension. If there is a twist in one or two spokes then it easily untwists on the road unbalancing the tension.

With double butted spokes you need to take extra care as the spokes want to twist as you tighten up. Light oil on threads and seating help. I use sticky paper to put little flags on the spokes before starting. If they all line up when stress-relieved at the end then none of the spokes are twisted. A professional builder should be able to do that by feel alone.

Were the spokes stress relieved?

How was the previous wheelset unlaced? If the spokes were just cut this can stress and mess up the rim.

This I don't know. Anyway to check?

Were the spokes stress relieved?

http://www.wheelfanatyk.com/blog/wheel-building-tip-no-4-how-to-pre-stress-your-wheel/

Is this what you mean by stress relieve?
I don't know if the mechanic done it the first time, but we've trued it a couple time more after that and didn't do anything like that.
Basically only truing and then balancing the tension.

Can't see any split nipples from the outside, but will check it too

Well it's been trued a couple of time now, so I would say it is persistent.

Definitely will consider all the input given so far!

1. Split nipples
   
2. Under/over tensioning
   
3. Twisted spokes caused by No stress relieving
   

Update:
So the mech unlaced the spokes and while I've never seen a twisted spoke it does seem twisted.
It is a bit bent.

No nipple crack though.

So I've changed the spokes and nipples with Richmond double butted. And will see how it goes.
NB: it's pressure relieved now.