Meeting : attendees's list not show if there are real values

It is just because your assignments are closed.
Just ckeck the "show closed" checkbox (wich is automatically checked when item is closed) to see the assignments.

Of course behavior is as expected.
Closing the meeting closes the assignments (same behavior occurs to activities)
Reopening the meeting does not automatically reopens the assignments.
To be able to close the meeting, you have to set all left work to zero, so assignements should be ended.
Moreover, when you reopen the meeting, we cannot know wetjer the assignment was manually closed (and then should stay closed) or was automatically closed when closing the meeting. So the rule is to keep the assignments closed.
Just re-open then if you need to (since V10.4 you can update many assignements in one step wil mutiple updates on new assignment form)
 

Just check the "show closed" checkbox.
Then you'll see assignments and will be able to reopen them