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Its Updated 7.1.2 and Still Facing Same Issue
I can totally relate with my nokia 6 phone I've had since the preorders got finally delivered so around 6 months..
Not a day has gone past that this phone hasn't had some issues, mostly apps crashing, taking minutes to load or while switching pages, launcher getting messed up by losing all widgets or randomly crashing(at least once a week), keyboard(or keyboards since I've tried like 4 different ones, apart from the original) being super slow to react, sounds not playing for notifications, background applications getting lost, incoming calls not being shown elsewhere but in the notification list...
But the latest issue with the phone losing absolutely all of its sounds with every level maxed out, even the ones being played when listening to music, watching youtube etc. totally gone, until I rebooted/shutdown + started ~3-4 times before the sounds started working again, this has made me start looking for an alternative and am not likely to return to HMD phones..
Oh and I've got the Oreo update, so I've got the endless notifications too..
I am extremely dissapointed with the phone. Those who have mentioned the issue I am in complete agreement with them.
I had none of the issue you had, on the contrary, best battery life since nokia n95. Update to oreo 8.0