Try to use an extra field for person name.

biscuit/apps/alsijil/forms.py

@@ -13,14 +13,13 @@ class LessonDocumentationForm(forms.ModelForm):
 class PersonalNoteForm(forms.ModelForm):
     class Meta:
         model = PersonalNote
-        fields = ['person', 'absent', 'late', 'excused', 'remarks']
+        fields = ['absent', 'late', 'excused', 'remarks']
+
+    person_name = forms.CharField(disabled=True)
 
     def __init__(self, *args, **kwargs):
+        kwargs.update(initial={'person_name': str(kwargs['instance'].person)})
         super().__init__(*args, **kwargs)
-        self.fields['person'].widget.attrs['readonly'] = True
-
-    def clean_person(self):
-      return self.instance.person
 
 
 PersonalNoteFormSet = forms.modelformset_factory(

biscuit/apps/alsijil/templates/alsijil/lesson.html

@@ -53,7 +53,7 @@
       </tr>
       {% for form in personal_note_formset %}
        <tr>
-        <td>{{ form.person }}</td>
+        <td>{{ form.person_name }}</td>
         <td>{{ form.absent }}</td>
         <td>{{ form.late }}</td>
         <td>{{ form.excused }}</td>