Participant on mute, yet I can still hear them

What do you mean by their own space? Are you referring to a Zoom Session or event space?

OK, @SamPeters . The person who picked them up may not be using the best sound settings for their environment.
If you ask them to look at their audio settings and change their audio profile to high, zoom will work harder to cut out background noise.
It has to be done at user level on the machine concerned.

John

@ExpertswhoJohn I think you misunderstand me. The user IS NOT in a setting where there are other users/ background noise.

@SamPeters, you can only hear from another Zoom user if they

1. Have their microphone on

2. Share their sounds from the screen share options.

3.  they are using a second device?

If they were muted, you would not hear them.

Exactly. That is why the situation is strange. They have the mute icon showing but can be heard. All other meeting attendees are muted. @ExpertswhoJohn 

I noted tonight that the callez headset. The microphone mute was muted, on the button,  and yet the microphone did work, when for 3 years this had not been the case.

Looks like a Windows update has stopped it from working.  MUTE it does not mute.

Gosh can not make sense.