Mic Controls not visible for one participant

Hi,

I have a participant who can enter my zoom meetings without the mic being under my control as the host. The mic icon is not visible on their zoom window, in the zoom window drop-down-list or in the participants list.  Where the mic control is usually displayed there is nothing.  And when I hover over the video control menu the Ask to Unmute options does not display. They also can still use their mic when I disable the Unmute Themselves option in the Security drop-down menu.

I can still hear them and they speak with the group without any problem, but I don't have any access to the mic controls and can't turn it off. I've asked them to turn the mic off, and they say they've turned it down on their end. 

Effectively, I have zero control over their wish to speak whenever they want.  Given I run a silent writing group, this opens up a security problem with zoom bombers.  Several of whom I've already had to deal with.  And my first line of defence being to turn off all the controls.  But in this situation I can't turn off their mic.

Has anybody else had this problem, and have you been able to prevent participants from entering the zoom room with total control over their own mic with the mic controls invisible?