What is Safe mode?
Safe mode is the emergency action to start WordPress without activating any plugins or themes. It helps you to investigate the issue or solve the errors which fail to get booting WordPress.
Starting WordPress in Safe mode
1. Navigate to [Emergency Action] menu under [Dev] menu on your website
2. Scroll down to the Safe Mode section
3. Check the type of Safe mode deactivate all plugins and/or changing the default theme.
Deactivate all plugins
Deactivate all themes
4. Then click the [Start container in safe mode ] button.
5. Log in WordPress and check safe mode is working.
Plugins
No plugins are activated.
Themes
Default theme is activated (WordPress 4.9's default theme is TwentySeventeen)