Cannot recognize (see or hear) participant, and versa

I created a conference URL as first user and stayed in the room. I selected everyone starts hidden, to avoid sharing our cameras by default.
A few minutes after a participant entered the room. But I couldn’t recognize that he entered, and versa, he couldn’t recognize that I’m in the room. I.e. there wasn’t a participants or moderators thumbnail showing up, even not in black.
When I left the room and joined again, we could see that everyone is here.

Client: Chrome

Anycould could explain what happened here?