Allow screen

I have just tried my first conference with 6 potential participants.
All are using various editions of windows and all were using Chrome.
All installed the Chrome extension.
All gave permission to use microphone and camera.
2 only got as far as the grey banner which says “Jitsi meet needs to use your microphone and camera. Select Allow when your browser asks for permissions.” and it just sticks there.
Grateful for advice.