Hmmm, well has the system been bled?
The "freezing" can be from many things, dirt, contaminates or symptoms of something lodged in the lines - Bleeding out the system may or may not help in dislodging the obstruction.
I was also thinking too, is your clutch pedal return spring - behaving ok? I mean it returns to up position (right?) - so it's supposed to "pull" the rod off the bottom of the cylinder and pull that fluid it pushed into the other cylinder back into itself - any lost fluid or heated up expanded rate fluid - simply "burbles up" to the reservoir tank as well as any excess.
There are two lines to one of the cylinders as a means to burp the system and allow for this exchange of fluid to occur.
The clutch isn't a perfect sealed system, it needs fluid and exchanges it with the mater cylinder for the brakes.
So my thoughts on this is to "dislodge" may require a trip to the shop for them to pull the lines and blow them clear then bleed the system to restore the clutch.
Its' the "key off" to Key on - and how that seems to clear the condition - is what has me stumped.
Here's is another scenario, say you are applying the Brakes, the Master cylinder is pressurizing the Brake side of the system - which if you work with me here, means that as you apply the brakes, your stop the reservoir from acting idly by as a "lake" keeping fluid in the system - the vanes and pistons that supply fluid to the brakes from the Master cylinder are now closed off - no fluid can enter into the system.
IF you have problems with the Power Assist brakes or in that area, the "restarting" of the vehicle can affect the Vacuum chambers ability to reset and release the pressurized fluid back into the master cylinder. IF the Brake pedal does not return full up, there may be a binding issue in the master cylinder and hence the "freezing" it's not from dirt, it's from "starvation" of the system to free up fluid for the other cylinder system, your clutch - to work with. Fluid simply cannot be released in enough volume to restore clutch operation because of what I mentioned earlier - the Hill Assist. So - I wonder if a diagnostic may be needed to follow the fluids in the system to determine the true fault.
To help you, you will need to look for and possibly observe as you dive your head under the dash - locate the Brake Pedal, there are two switches on a lever towards the front Knee pad just below the steering wheel.
IF those two switches are NOT working right, I can see why you have this issue and then the switches themselves may need some simple adjustment to realign their aspect and let the brake system work separately from the Clutch - for one of the switches handles the Brake Light (rear brake light) the other is a "condition" light that also works but handles Hill Assist and the ability to even "start" the vehicle.
One last aspect to add to this, deals with a "Hydrostatic lock" condition. It's where a sealed system can't operate because both side of a moving piston contain the same pressure - under pressure - causing the fluid to stay static or "locked"..
To further Read...
Hydrolock - Wikipedia
The Clutch in order to work with the Brake Reservoir - has to be able to remove fluid from that reservoir and put it back again.
IF Hill Assist or another condition like vacuum seal of the Power Assist assembly of the Brakes, prevents the Clutch from releasing fluid back into the reservoir- the pedal becomes stiff and "stays" where you put it, if you put too much pressure on it, it will leak and blow a seal just to relieve pressure.
It can also be "reciprocal" as in the reverse can also be true, you can generate an air leak when the system needs to have pressure applied in a given direction in a sealed system - the pressure itself becomes the static event, because an air leak allowed the other side of the system to relieve pressure and so the means to return the pressure to make it equalized, is now gone, the piston remains stuck in that static position until the pressure on the side of the NON-Air leak can be released and the fluid in that side be allowed to return to normal balance.
As you can see, each Scenario discussed, from wrong DOT-type fluid onto the Debris in the Shifter Assembly at the Transmission housing, onto the Shift lever assembly in the Dash, onto Electrical failure to track the Hydraulics of the system properly generating lock conditions onto air leaking into the system preventing the fluid from finding equilibrium
Each one is more sinister than the previous, as well as more involved in tasking and time-consuming in labor $$$...
There are several avenues of thought we could take this, but you own the car and have the best idea as to what's been done to it - so in working thru your scenario of Clutch acting up - the typical Service station will be at odds wondering what could cause the condition.
I would be curious to know, that if you turn-off Traction control - as safe as you can be, conditions override this choice - but run your vehicle normally thru it's paces with Trac OFF - and see if the condition keeps re-occurring.
IF it doesn't - or you can't seem to recreate the problem - you have a potential air leak in your system or your Brake Booster side of your Master Cylinder Brake system - needs to be checked. You changed the conditions of the systems operation - less usage of a system in this system - if this clears up that problem, your problem was within that sub-system.
