When a teacher accesses a BigBlueButton activity in a course with separate groups enabled, the teacher has the choice of the list of groups and on top (selected by default) "All participants".

This is misleading. The truth is that not all participants will be in the room, but only those who are not in a group.

The language string comes from core, where it is used at least in forum. There it makes sense: when you choose "All participants" in the group chooser, your forum message will be shown to all participants, but not in the BBB session.

I know this is more or less illustrated by a (default yellow) text, saying "There is a conference room for each group and you have access to more than one. Be sure to select the correct one." above it, but even with reading that text carefully it could still be misunderstood.

Steps to reproduce:

• Create a course using separate groups
• Create a few groups with users
• Create a BBB activity
• Access it as a teacher who is not a member of any group
• You'll see the "All participants" label in the drop down -> select this and start session
• Join session with one of the students in a group -> teacher and student will not be in the same session.

Expected behaviour:  all participants should be able to see each other.

My suggestion is to create a new language string for this drop down group selector and label it "Participants not in a group" or something similar, so the behaviour is better represented by the string.

Another, more complicated and maybe better fix could be that All participants has the same behaviour as in Forum, being all participants have access to the room, regardless of what group they are in.

This weird behaviour is also described in this documentation document: https://support.bigbluebutton.org/hc/en-us/articles/1500005216221-How-does-grouping-work-

As far as I could find, it is not documented on https://docs.moodle.org/400/en/BigBlueButton