magento 2 product changes not showing in website

we are a website development company and outsource work as required. We have a server configured with nginx and varnish for magento 2 websites (multiple separate websites, using separate accounts in a Virtualmin hosting environment). Issue: When a change is made to a product or general content in the admin, the change is saved in the admin but is not reflected in the website. If Varnish is restarted the changes are then seen. This is not how Magento with Varnish is supposed to work. Required: When a product or general content is updated only that general content, product or the changes made to that product are to be purged out of the Varnish cache. The entire Varnish cache must not be purged nor Varnish restarted. This must happen automatically by the Varnish, Magento, Enginx configuration. NOTES: - ideally you should have access to a similar server that is working so you can use the configurations from that server - you will also have the option to change the installed version of Varnish if needed - the server was setup as per magento's website instructions - changes were made for multiple websites to be supported - Although we do not know why this is happening we believe you will need to understand and be able to make changes to Varnish, Magento and / or Enginx configuration settings and files. You will get: - full access to the entire server - full access to websites: hosting and admin Please provide a cost and time to complete. Proposed Engagement process: - if selected, you will be asked to accept the project before a milestone is made - you will then be given server access so you can look into the issue further - you then confirm you can do the project and the milestone is then created - We release full payment upon completion.