Screen locks during a call

[Marty89]

Hello, in my family we have two Nokia 8 phones and both of them have a same issue during calls. If I make a call with original Nokia flip cover attached, the phone always locks itself during a call after the set time in lock screen settings. Without the cover the screen goes black but lights up when I put it further from my face. My friend has a Nokia 5 with flip cover and no issue here.