Unexpected shut downs

Hello,
I’ve had my Fairphone a month; all software updates have installed fine. I have an issue where the phone shuts suddenly for no apparent reason and will not respond to pressing the on/off button.I have to take the cover off, remove the battery and put it back in before it will reboot. I had a couple of these early on, but now I am getting them once a day. Has anyone else had this issue or know what I can do about it? Doesn’t seem to be related to a particular app…
Thanks,
Chris

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