I recommend to follow the troubleshooting steps below.
- Use the latest software versions : make sure WordPress, your theme and plugins are all updated to their latest versions.
- Cache plugin : if you use a server cache or cache plugin, clear it’s cache content and disable caching via it’s settings.
- Browser :
- Check for plugin conflict : Install the WP official Health check plugin. Activate the troubleshooting mode. Then deactivate all of your plugins. If it fixes the issue, re-activate your plugins one by one, until you identify the plugin in conflict.
- Child theme : activate the parent theme if you use a child theme
- Theme problem : try to activate a WordPress default theme ( Twenty … )
- Javascript : make sure you did not insert custom javascript code ( like analytics, subscription popup… ), for example in a widget, that could break your site.