Keeping Chat Notifications banner on screen until dismissed

We are using Zoom for church meetings, so that older or sick ones can still participate in the meeting. At times there is a need to communicate with the operators of the audio-visual system in the church and personal Chat messages work for that purpose but the chat preview only stays visible for a few seconds before being replaced with a number. Under Team Chat in Settings, there is an option to "Show notification banner on screen until dismissed", but, although this is ticked, the preview message still disappears. Does this have to be activated somewhere else?

Thanks, 

Allan