S20 ultra goes into silent mode

[Suz20]

this is most annoying I have kissed very important phone call last night rom hospital because I phone keeps putting its self into silent mode pmease someone sort this out 

[Gar0504]

mine does not do that. have you good a do not disturb schedule active?

[Members_Ks8NtN4]

late at night phone thinks you're sleeping

[AndrewL]

@Suz20: It sounds like Do Not Disturb Mode may be active. To check this, please go to Settings > Notifications > Do Not Disturb, and toggle the switch next to it so it moves to the left and greys out. I hope this helps. 

[zc]

I've had similar problem with S7 and A53.  Others report same problems. My issue seems to be happening after a phone call I answered. Next call I don't know about because it went to silent for ringer volume.  And NO it is not the Do Not Disturb setting.  I can't predict when the issue will happen.