The Currency Switcher includes a debug mode that logs all the attempts to resolve a visitor's geolocation. Please follow the steps below to enable and view the log.
1. Enable debug mode in the Currency Switcher settings
You can enable the debug mode by going to WooCommerce > Currency Switcher > Support. Simply enable the option and save the settings. The page will also show you where you can find the log file generated by the Currency Switcher.
2. Test the geolocation
Using a VPN and an incognito/private browsing window, visit your site from several locations. This will add entries to the log file, showing the IP address and the resulting country and currency.
3. Review the debug log
You can find the log file at the location displayed at step #1. Since WooCommerce 3.x, you can also view the log file by going to WooCommerce > Status > Logs. The example below shows a sample log. It was taken from a local server, not connected to the Internet, and it shows that the IP address (in this case, "::1", which means "local host") could not be resolved to a country.
If you see the same IP address for many visitors, then it means that your site is behind a reverse proxy that masks your visitors' real IP addresses. In such case, you can contact your hosting provider to get the real IP address passed to your site.