Hi Philip, I did attempt to address your questions; maybe it went directly to your email since I hit "Reply to author"?
Assuming you're asking about the new NB, I'll answer with that in mind.
Question: If I turn random back on, will it assign just newly signed up users to one of the groups at random going forward?
If you don't assign users to a section, they will be left without a section, so they won't be able to see any comments from any of the other sections.
Question: Is there any issue with my changing assigned sections even after users have commented on other user's posts? Will they no longer see the post they commented on if their sections are different now?
Even if you change a student's section, they will still be able to see their own comments. However, they won't be able to view replies they made to their peers' comments that are in other sections.
Question: Is it normal that we can't see what section students are assigned to in the properties "section" page?
In the new version of NB you can see the sections and modify them under the "Users" tab. In order to modify the sections you first "Download Students CSV" then modify that, after that upload the csv again and the changes will be reflected.
Hope that helps!
Jumana