While giving a new quiz with respondus lockdown browser (not proctoring) I found myself wanting to communicate with several students, but there was no way to do this other than email, they responded after they submitted the quiz, so my communication was a failure.
In that case, I needed to communicate with specific students, but I can imagine students finding a mistake in a quiz and asking a question. In the classroom I just post a correction to an equation on the board. If they could message questions to the moderating page, and if I could message specific students or all students with pop-ups in their lockdown browser that might resolve the issue. With a timed-quiz, and no-backtracking allowed, they may need information within a minute or so.
Thanks to @Steven_S for his response to my original post in the new quiz forum "how to communicate with students taking respondus lockdown quiz" I'm new at this, not sure how to link to the post