Oil level dropped to 86% from full - a week after collection

[Firstvolvo111]

OK so we picked up our new petrol 2021 volvo xc40 t3 (approx 18k miles) approx 2 weeks ago, when we test drove the car we noticed that the oil level was showing full, no issues.

On the day the car was collected it had been serviced by the dealership, so I presume the oil level checked and if necessary, topped up.

Approx a week later, I was looking for something else on the settings and noticed that the oil level had dropped 12 bars, we contacted the dealership straight away being under warranty who advised us to take it to an independent garage, and check for leaks. We did this and the mechanic said that he could see no evidence of external leaks but could not rule out an internal one, albeit seeing no obvious signs.

Weve taken the car back to the dealership and their mechanic confirmed oil had been lost and it was now 86%, but again on inspection can't find any obvious defects. I believe they are going to test drive the car tomorrow.

I am looking for advice, if the dealership can't find any obvious fault, and the level hasn't dropped following their test drive, is it still a concern? Would you push / suggest for us to get a diagnosis directly with volvo? I don't know if it is safe to drive.

Is this a common fault? Can anyone think of any reason that could have caused it?

Thank you for any advice,