This can have several causes. Consider, for example:
- Your internet connection
- The quality of your WiFi
- The type of device you are using
- Which browser you are using
You can try to:
- Clear your browsing data (cookies/cache)
- Switch from WiFi to a wired connection
- Use a different browser (preferably Google Chrome)
- Log in from another device
- Restart your modem/router if it turns out your internet connection is slow