diff --git a/lms/djangoapps/verified_track_content/models.py b/lms/djangoapps/verified_track_content/models.py
index 4b5b4f6134..20373aa377 100644
--- a/lms/djangoapps/verified_track_content/models.py
+++ b/lms/djangoapps/verified_track_content/models.py
@@ -49,7 +49,11 @@ def move_to_verified_cohort(sender, instance, **kwargs):  # pylint: disable=unus
                     'verified_cohort_name': verified_cohort_name,
                     'default_cohort_name': random_cohort.name
                 }
-                log.info("Queuing automatic cohorting for user '%s' in course '%s'", instance.user.username, course_key)
+                log.info(
+                    "Queuing automatic cohorting for user '%s' in course '%s' "
+                    "due to change in enrollment mode from '%s' to '%s'.",
+                    instance.user.id, course_key, instance._old_mode, instance.mode  # pylint: disable=protected-access
+                )
 
                 # Do the update with a 3-second delay in hopes that the CourseEnrollment transaction has been
                 # completed before the celery task runs. We want a reasonably short delay in case the learner
diff --git a/lms/djangoapps/verified_track_content/tasks.py b/lms/djangoapps/verified_track_content/tasks.py
index fce883d0b4..bdaa943f46 100644
--- a/lms/djangoapps/verified_track_content/tasks.py
+++ b/lms/djangoapps/verified_track_content/tasks.py
@@ -2,6 +2,7 @@
 Celery task for Automatic Verifed Track Cohorting MVP feature.
 """
 from django.contrib.auth.models import User
+from django.db.utils import IntegrityError
 
 from celery.task import task
 from celery.utils.log import get_task_logger
@@ -30,31 +31,43 @@ def sync_cohort_with_mode(self, course_id, user_id, verified_cohort_name, defaul
         enrollment = CourseEnrollment.get_enrollment(user, course_key)
         # Note that this will enroll the user in the default cohort on initial enrollment.
         # That's good because it will force creation of the default cohort if necessary.
-        current_cohort = get_cohort(user, course_key)
+        try:
+            current_cohort = get_cohort(user, course_key)
+        except IntegrityError as integrity_error:
+            # It is quite common that get_cohort will throw an IntegrityError. This happens
+            # when 2 celery workers are both handling enrollment change events for the same user
+            # (for example, if the enrollment mode goes from None -> Audit -> Honor); if the user
+            # was not previously in a cohort, calling get_cohort will result in a cohort assignment.
+            LOGGER.info(
+                "HANDLING_INTEGRITY_ERROR: IntegrityError encountered for course '%s' and user '%s': %s",
+                course_id, user.id, unicode(integrity_error)
+            )
+            current_cohort = get_cohort(user, course_key)
+
         verified_cohort = get_cohort_by_name(course_key, verified_cohort_name)
 
         if enrollment.mode == CourseMode.VERIFIED and (current_cohort.id != verified_cohort.id):
             LOGGER.info(
                 "MOVING_TO_VERIFIED: Moving user '%s' to the verified cohort '%s' for course '%s'",
-                user.username, verified_cohort.name, course_id
+                user.id, verified_cohort.name, course_id
             )
             add_user_to_cohort(verified_cohort, user.username)
         elif enrollment.mode != CourseMode.VERIFIED and current_cohort.id == verified_cohort.id:
             default_cohort = get_cohort_by_name(course_key, default_cohort_name)
             LOGGER.info(
                 "MOVING_TO_DEFAULT: Moving user '%s' to the default cohort '%s' for course '%s'",
-                user.username, default_cohort.name, course_id
+                user.id, default_cohort.name, course_id
             )
             add_user_to_cohort(default_cohort, user.username)
         else:
             LOGGER.info(
                 "NO_ACTION_NECESSARY: No action necessary for user '%s' in course '%s' and enrollment mode '%s'. "
                 "The user is already in cohort '%s'.",
-                user.username, course_id, enrollment.mode, current_cohort.name
+                user.id, course_id, enrollment.mode, current_cohort.name
             )
     except Exception as exc:
         LOGGER.warning(
             "SYNC_COHORT_WITH_MODE_RETRY: Exception encountered for course '%s' and user '%s': %s",
-            course_id, user.username, unicode(exc)
+            course_id, user.id, unicode(exc)
         )
         raise self.retry(exc=exc)
diff --git a/openedx/core/djangoapps/course_groups/models.py b/openedx/core/djangoapps/course_groups/models.py
index 14ce7a7fe8..3c3cad5791 100644
--- a/openedx/core/djangoapps/course_groups/models.py
+++ b/openedx/core/djangoapps/course_groups/models.py
@@ -90,7 +90,7 @@ class CohortMembership(models.Model):
     def save(self, *args, **kwargs):
         self.full_clean(validate_unique=False)
 
-        log.info("Saving CohortMembership for '%s' (id=%s) in '%s'", self.user.username, self.user.id, self.course_id)
+        log.info("Saving CohortMembership for user '%s' in '%s'", self.user.id, self.course_id)
 
         # Avoid infinite recursion if creating from get_or_create() call below.
         # This block also allows middleware to use CohortMembership.get_or_create without worrying about outer_atomic