I have the same issue.
Apple believes their tool more than their customers!!
Contacted online customer support, they ran their diagnostics tool and found no problem, asked me to come directly to apple store gor service.
Went to store for repair, they did run same diagnostics and no issues found. I was abl to reproduce the problem there itself ( without case or screen guard), but they were not even ready for demo.
Contacted customer support again, he accepted the issue(said he added the notes as he too observed it) and asked me to ship my phone to factory repair center in california, within 4 hours of receiving my device, they updated as we are not able to duplicate the issue and shipping back the device.
I believe either they dont have any skilled tecnicians to reproduce a simple issue or they dont want to address this issue.
In any case, i have lost my money to Apple.