Random screen locks while using phone

This happens to me at least once a day. I'm simply using my phone and screen goes black for like 2 seconds. Then the locksreen shows up but it's black for a second or two and the time says 00:00 for a fraction of a second. After that it stays on my lockscreen and obviously I have to unlock to keep using it. It happens very randomly. Not at the same time everybody. Not using the same app. It just happens randomly. I haven't installed anything recently or done any changes to any setting that could be causing this issue to happen.