I understand you're looking for a sophisticated, innovative and fully documented code solution based on the challenge description provided earlier. Here's a high-quality code implementation using Python, Flask, and SQLAlchemy to design a scalable and robust e-learning platform. Ensure you have installed the required libraries: Flask (web framework), Flask-SQLAlchemy (ORM for Flask), Flask-Migrate (for database migrations), Flask-Caching (for caching), and PyJWT (for token-based authentication). You can install them using:

```bash
pip install Flask Flask-SQLAlchemy Flask-Migrate Flask-Caching PyJWT
```

Here's the project structure:

```lua
project/
├── app.py
├── config.py
├── models.py
├── schemas.py
├── auth.py
├── main.py
└── requirements.txt
```

Below you will find an example of an implementation for a specific microservice, the User Service.

File: [app.py](https://app.py)

```python
import os
from flask import Flask, request, jsonify
from flask_migrate import Migrate
from flask_caching import Cache
from config import Config
from models import db, User, Course, Session
from auth import bp as auth_bp
from main import bp as main_bp

def create_app():
    app = Flask(__name__)
    app.config.from_object(Config)
    app.register_blueprint(auth_bp)
    app.register_blueprint(main_bp)
    db.init_app(app)
    Migrate(app, db)
    cache = Cache(app)

    @app.route('/')
    def index():
        return "Welcome to the e-learning platform!"

    return app
```

File: [config.py](https://config.py)

```python
import os
from dotenv import load_dotenv

load_dotenv()

class Config:
    SECRET_KEY = os.environ.get('SECRET_KEY') or 'your-secret-key'
    SQLALCHEMY_DATABASE_URI = os.environ.get('DATABASE_URL') or 'sqlite:///e-learning.db'
    SQLALCHEMY_TRACK_MODIFICATIONS = False
    CACHE_TYPE = 'simple'
    JWT_SECRET_KEY = os.environ.get('JWT_SECRET_KEY') or 'your-jwt-secret-key'
    JWT_ACCESS_TOKEN_EXPIRES = False
```

File: [models.py](https://models.py)

```python
from datetime import datetime
from flask_sqlalchemy import SQLAlchemy
from schemas import ma

db = SQLAlchemy()

class User(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    username = db.Column(db.String(80), unique=True, nullable=False)
    email = db.Column(db.String(120), unique=True, nullable=False)
    password = db.Column(db.String(128), nullable=False)
    courses = db.relationship('Course', backref='user', lazy=True)
    sessions = db.relationship('Session', backref='user', lazy=True)
    created_at = db.Column(db.DateTime, default=datetime.utcnow)
    updated_at = db.Column(
        db.DateTime, default=datetime.utcnow, onupdate=datetime.utcnow)

class Course(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    title = db.Column(db.String(100), nullable=False)
    description = db.Column(db.Text, nullable=True)
    user_id = db.Column(db.Integer, db.ForeignKey('user.id'), nullable=False)
    sessions = db.relationship('Session', backref='course', lazy=True)

class Session(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    title = db.Column(db.String(100), nullable=False)
    description = db.Column(db.Text, nullable=True)
    user_id = db.Column(db.Integer, db.ForeignKey('user.id'), nullable=False)
    course_id = db.Column(db.Integer, db.ForeignKey('course.id'), nullable=False)
    created_at = db.Column(db.DateTime, default=datetime.utcnow)
    updated_at = db.Column(
        db.DateTime, default=datetime.utcnow, onupdate=datetime.utcnow)

ma.init_app(db)
```

File: [schemas.py](https://schemas.py)

```python
from marshmallow import Schema, fields, EXCLUDE
from models import User, Course, Session

class UserSchema(Schema):
    class Meta:
        unknown = EXCLUDE

    id = fields.Int(dump_only=True)
    username = fields.Str(required=True)
    email = fields.Str(required=True)
    password = fields.Str(load_only=True, password=True)
    courses = fields.Nested('CourseSchema', many=True, load_only=True)
    sessions = fields.Nested('SessionSchema', many=True
```