a leak would only occur/be called a leak if your IP between re-connections becomes known to your ISP
I’m not sure what you mean by ‘your IP being known to your ISP’, my ISP always knows what my IP is, they are the provider of it after all. In any case, my real IP does become known to any server that is connecting to my computer during the server switch. The way I found out this was happening was by refreshing a ‘what’s my IP’ test page while switching servers and it would always show my real IP during this time (no exceptions).
So if you are ever getting IP blocked and switch servers, you are directly exposing your real IP to the service during the re-connection. This is not the desired or expected behavior from a VPN, especially one that advertises itself as a privacy oriented choice.