The connection pool in Reactor Netty 0.9 was switched from elastic to fixed 500 connections (per host), see https://github.com/reactor/reactor-netty/issues/578.
By default the WebClient picks up this default, even if ReactorResourceFactory is plugged in, as Spring Boot does, because useGlobalResources is true by default. However if global resources are turned off, then we have our own default supplier that does ConnectionProvider.elastic("webflux"). This should be changed to align with Reactor Netty.
Further in 0.9.5, ConnectionProvider.elastic and ConnectionProvider.fixed are both deprecated. We can use ConnectionProvider.fixed("webflux", 500) in 5.2.x and switch to ConnectionProvider.create in 5.3.