Lumia lost ringtone and other tones

[caveman38]

I have 2 Lumias - 640 &735. Both run W8.1 and suffer the same problem. I lose sounds, the most important being incoming call alert. I know they have disabled as the keyboard key clicking disappears.
The way to remedy this is a hard boot but this is becoming tiresome and I'm missing calls when I'm not aware.
Why is this happening and what is the cure, please. Many thanks if you can help.

 

[abhishek singh21]

I would insist that you upgrade both your devices to windows 10 mobile using the upgrade advisor app.

 

[caveman38]

Thank you for the reply. Is that advice based on the fact that you know that it WILL cure the problem. Or is it a good starting point.