Hi there,
The fact that the price disappears a while after the 0 is entered as a product price sounds weird.
I wasn’t able to replicate this behavior on my test site.
Perhaps there’s a limited stock quantity and there are no more products left? Although in that case an Out of stock message would appear instead.
Issues like this may be caused by either a conflict with your theme or with another plugin. You can read more about plugin and theme conflicts here:
https://docs.woocommerce.com/document/woocommerce-self-service-guide/
The best way to determine if the issue is being caused by a theme and/or plugin is to do the following:
1. Temporarily switch your theme back to the Storefront or Twenty Seventeen Theme.
2. Disable all plugins except for WooCommerce.
3. Test to see if the issue has been resolved.
If that resolves the issue, then one-by-one you can switch back your theme and re-enable your plugins, testing in between, until you find the one causing the conflict.
One tool you can try is Health Check since it allows you to do the test without affecting visitors of your site.
If doing this on your live site is not possible, you can create a duplicate site. We suggest using WP Staging if your hosting provider does not offer a staging server as an option.
