Just two more suggestions:
Reboots have sometimes been caused by a slightly oversized battery bay – i.e. the battery doesn’t sit still enough and loses contact. You can check if this is the case if you open the back cover of the phone and check if you are able to cause a reboot by trying to move the battery towards the battery bay’s bottom end. This can easily be fixed by attaching a bit of folded paper at that end.
And in general: You mentioned NE Italy – if you are near Padova, there is a Fairphone Angel in that town (might be helpful in the future 
).
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