I have a very fast Magento 2 backend, I have configured Varnish caching. When I save any product, it takes about 20 seconds to save while loading the product edit page goes very fast. Saving category pages are also slow while saving customer data it's very fast. So it must be something with the cache invalidation I think.
The moment I switch back to inbuild cache, it's very fast again. No changes in IP's etc. I checked the cache purge IP's but it looks like there is no issue.
I have upgraded from Magento 2.1.9 to 2.3.2. Probably there's an issue. I have a fresh Magento 2 installation, on the same server that doesn't have that problem.
Also, my Varnish server is a seperate server. I host them both in Azure. They are both in different subscriptions, networks are peered. At first I thought that the problem could be a network issue but than the second Magento 2 installation should have the same problems. Both server can reach each other on port 80 and 443.
I checked varnishncsa and varnishlog, I can't find any errors.