In case you have recently proceeded with any changes to the CNAME record added for your school, you may need to clear the cache of your DNS in order for your browser to properly "load" your custom domain.
You can follow these steps:
For Windows (10.8 & 8.1)
1. Navigate to the desktop. (From Home, tap or click the Desktop tile).
2. Right-click the Start button (the Windows logo in the lower-left).
3. Choose Command Prompt (Admin).
4. When asked whether to allow Command Prompt to make changes to your computer, select Yes.
5. Type "ipconfig /flushdns" and press Enter.
6. Type "ipconfig /registerdns" and press Enter.
7. Type "ipconfig /release" and press Enter.
8. Type "ipconfig /renew" and press Enter.
9. Type "netsh winsock reset" and press Enter.
10. Restart the computer.
For Mac OS X
1. Close all browser windows.
2. Click Applications → Utilities → Terminal.
3. In the Terminal window, type in the corresponding command mentioned below for your Mac OS X version.
4. Enter the Mac’s password, if prompted.
5. Press the enter key and the DNS cache should be flushed.
- macOS Big Sur (11.0.1): sudo dscacheutil -flushcache; sudo killall -HUP mDNSResponder
- macOS El Capitan (10.11), Sierra (10.12), High Sierra (10.13), and Mojave (10.14): sudo killall -HUP mDNSResponder
- macOS Yosemite (10.10): sudo discoveryutil udnsflushcaches
- macOS Mavericks (10.9), Mountain Lion, and Lion (10.7 up to 10.9) : sudo killall -HUP mDNSResponder
- OS X 10.6 and older: sudo dscacheutil -flushcache
For previous versions of Windows or more information about this process, you can check out this article and in the case, of Mac OS, you can find useful information here.