I understand your point of view. But if I can try to repair my phone without voiding the warranty, I will try. Even if it should be the job of Cordon or FP. If the support team had hinted you to try this, would you have done it? If yes, well I don’t see really the difference as a result.
You experience this issue. You don’t have to repair it, you can keep your issues if you want. The thing is you don’t, you would like them to be solved. And for this, you have two solutions: asking the repair team, or doing it yourself. Support and repair team didn’t manage, I’m truly sorry, but you can still try yourself.
I understand you would like Fairphone to repair this defect because your phone is under warranty, but as a result it will not change much to do it yourself.
@jande doesn’t seem to be the only one to experience this. Could you ask the responsible team at Fairphone to investigate this problem with @Moaxle’s solution, and try to understand if there is a defect or not? I don’t have any idea what the problem is, but a few people seem to have had this problem with this as solution.