All credit to users @Maksim and @user1535610956109 for this find; quoting them below:
"This is probably due to poor memory management of the phone. I don't know what cause is, but i know how to reliably reproduce the issue.
You can download MemoryPump or similar memory filler application.
I run it on: Google Pixel 2, Samasung S4 mini, Huawei P9 lite. When I press "allocate all memory" all of them just simply shut down this application.
BUT Nokia 6.1 becomes completely unresponsive and reboots after couple of minutes. Please verify if your phones do the same."
"I also have the stated problem even after an update. This is ridiculous.
I captured related problem on video on youtube https://www.youtube.com/watch?v=pf-b08BwmVk&feature=youtu.be
Check it out. If you have same problem let me know in comments. May be there is hardware bug in some phones and we can get phone replaced. "
"Me too. These issues have been there since launch and Nokia does nothing to fix them. I think it might be related to bad memory management and badly build background services that make the phone freeze. At least for me there's sometimes notification about the service that has stopped, but not always. Usually when the phone freezes when doing something related to camera, it doesn't show anything. But when it hangs randomly (like it does few times a day), it tells always different component that has stopped, like seen in this photo "
I can reproduce the issue shown in the video on my phone as well.
Hello, the same situation tomorrow. It's very frustrating, it happens many times a day, most often in the morning when I pick up my phone, I can not use it for a few minutes. I honestly do not know what to do next.
I also bought my boy a Nokia 6.1, and now I'm disappointed. The wife has Nokia 6 and does not have these problems. We are Google Nexus users and we switched to Nokia, but disappointment is great.
Does your wife have the 4GB version by any chance?
that would explain why she has more headroom and thus isn't having the issues. I suspect if you use an app to fill the RAM on hers it would crash as well