What causes my error "Illegal choice in Sorted by element"? Drupal 7.50 commons

The following error shows dozens per minute when I run drush ws --tail,  but there are no reports of users encountering errors or features that are non-operational. Does anyone know what could be causing this? Reporting for anonymous user.

error     form  Illegal choice  in Sorted by element.


Below is a screenshot of one of the errors, for detail.


Below is a screenshot of part of the page content that might be generating the problem, from admin/reports/dblog.


The error seems to be affecting more than one group or all of our groups. Here is an example URL from another entry:
http://example.com/groups/oregon?sort_by=&amp;sort_order=DESC&amp;page=0,0,1

Here is the Commons Browsing Widget View Sorting Criteria:
I was able to figure out what view was being used on group pages (The Commons Browsing Widget) and see that there were three sorting criteria. One of them is the Radioactivity module. 

I checked the general status report (admin/reports/status) to see that there was an issue with RadioActivity module. 

I removed this sorting feature for now, but it should work now that I cleared up the issues with the module. I guess no one could have known that this was the cause. I'm keeping this up in case anyone else finds it helpful.