Superb coolant leak - its a mystery....

I have a 2021 SEL 200hp auto Diesel estate from new 14/5/2021. Since then it has been with the main dealer for 25 days spread over a number of visits trying to find the cause of the coolant leak. It was diagnosed to come from a faulty bleed nipple on the secondary radiator in November and was fixed. Today whilst on business, miles from home the warning light came on and I had to stop by the roadside. Skoda Roadside dispatched a specialist who topped up the system with 600ml of water and completed a pressure test. All was fine and there were no signs of a leak anywhere. This is a contract lease car, there is the possibility that the coolant is going through the EGR Valve but this had been discounted by the dealer. It is clearly going somewhere. Question is - has anyone else had this experience and do I reject the car as not being fit for purpose. This issues started 3 days after i collected the car from the dealer and I have a record of every interaction with the Skodas dealer. Appreciate your feedback and advice.