iPhone apps open randomly

My son has the iPhone 12. He had the XS previously which I now use. I gave him my upgrade to the 12. On different phones he has encountered what he says is apps opening randomly albeit infrequently. He describes it as being in some other app (browser, youtube, whatever) when he touches the screen for instance to open a video in Youtube via the app or browser, let's say, one of the basic pre-installed apps opens (weather, files, apple watch, find my phone).

This has been exasperating as I have not been able to duplicate it but he swears it happens and describes as I have done here. He also says it happens only when he is signed in with his apple ID. Only once he said it happened when not signed in.

Since I took his phone, the XS, I have not experienced that. We wiped the phones, restored the phones, updated the phones and he says it still happens. I had him wipe the phones again and slowly download whatever apps etc. he uses. Wait two weeks and if nothing happens install the next app and so forth.

This has been going on across two different phone models and different iOS updates.

He claims it started again and now refuses to use the phone. Is this an issue that has occurred with other users? What could cause this? How could it occur across different devices?