manytomany and manytoone relationships to the same table make sure to set relatedname if you use relationships to the same table
from django.db import models


class User(models.Model):
    username = models.CharField(max_length=20)


class Issue(models.Model):
    num = models.IntegerField()
    cc = models.ManyToManyField(User, blank=True, related_name="test_issue_cc")
    client = models.ForeignKey(User, models.CASCADE, related_name="test_issue_client")

    class Meta:
        ordering = ("num",)

    def __str__(self):
        return str(self.num)


class StringReferenceModel(models.Model):
    others = models.ManyToManyField("StringReferenceModel")