iPhone 11 lockscreen keeps freezing, camera greyed out

I don't know what keeps freezing my iPhone 11's lock screen.

It all started a month ago with the home screen that didn't always react properly. At first I didn't notice it (when typing a letter it didn't register), but it became more noticeable after a few days. Then the screen didn't work anymore. So I thought I needed a new screen. I did a hard reset and the problem was fixed. But then the problem changed to the lock screen.

When the lock screen freezes the camera is also greyed out. The side buttons keep working (so you can do a soft reset). It's impossible to put it in DFU mode since you have to connect it to a computer, but the iPhone always asks to accept the connected device and since the screen doesn't work...

When a bluetooth device is connected (headphones or car) the music player doesn't work: you see which song should be playing, but it doesn't start (even though it is playing).

After max 24h the iPhone suddenly works again.

I've seen similar issues in these conversations: iPhone 11 frozen lock screen and greyed o… - Apple Community, iPhone 11 frozen on Lock Screen . Camera … - Apple Community, iPhone 11 touch screen not working - Apple Community. => I've only seen this specific problem on an iPhone 11.

The typical answers (HOW TO FIX A FROZEN SCREEN etc) don't work. I've worked 5 years for an Apple Premium Reseller and Service and I can't work my way around this problem.

I've already did a hard reset (when the iPhone did work again) twice. The first time I reinstalled my back up and the problem occurred again. The second time I didn't reinstall my the back up. The problem didn't happen for over 2 weeks. Then suddenly it happened again.

I've now deleted two apps (Ultimate guitar: chords & tabs and GuitarTuna) hoping one of these apps was the issue.

Can anyone tell me what to do? The iPhone has still a few weeks of warranty, but I think it's a software problem, so I can assume that Apple won't accept it as a warranty issue.

Or could it be the screen (hardware?).

Regards,

Angelo