🐛 Bug Report

Scrolling causes a noticeable stutter on Docusaurus v2 websites

To Reproduce

1. Go to the docs section on the Docusaurus v2 website
2. Scroll to the top of the page
3. Attempt to scroll further upwards

Expected behavior

Docusaurus v1

Maximum CPU Usage: 22.0%

• Timers
  • 5 × setTimeout
• Events
  • 44 × scroll

Actual Behavior

Docusaurus v2

Maximum CPU Usage: 96.1%

• Events
  • 160 × wheel
  • 42 × scroll
  • 7 × message
  • 3 × mousemove
  • 2 × pointermove
• Observers
  • 889 × IntersectionObserver

Your Environment

• Public site url: https://v2.docusaurus.io
• Docusaurus version used: 2.0.0-alpha.72
• Environment name and version: Safari 14.0.3 (14610.4.3.1.6)
• Operating system and version: macOS 10.14.6