reset course group counters

db/migrate/20191028025241_re_counter_course_groups.rb

@@ -0,0 +1,7 @@
+class ReCounterCourseGroups < ActiveRecord::Migration[5.2]
+  def change
+    CourseGroup.find_each do |group|
+      CourseGroup.reset_counters(group.id, :course_members_count)
+    end
+  end
+end