To troubleshoot why your email folders are not syncing across devices, try these steps:

1. Check your email account settings in each device and ensure they are set to sync automatically.

2. Double-check that you are signed in to the same account on your other devices.

3. Disable and re-enable folder syncing for each device.

4. Close any running apps and then restart the device.

5. Update the mail app to the latest version available in your device’s app store.

6. Powercycle your devices, i.e., turn them off and then turn them on again.