chain.filter(exchange).doFinally( __ -> { 
    requestHub.popScope()
...
})
.doFirst {
...
    requestHub.pushScope()
...
}

chain.filter(exchange).doFinally( __ -> {
    ...
    transaction.finish()
})

class CustomSentryFilter: WebFilter {
    override fun filter(exchange: ServerWebExchange, chain: WebFilterChain): Mono<Void> {
        val hub = exchange.attributes.getOrDefault(SentryWebFilter.SENTRY_HUB_KEY, null) as IHub
        hub.configureScope { scope ->
           // something change outside of Mono flow
        }

        return Mono.just(1)
            .doOnNext { 
                hub.configureScope { scope ->
                   //something change in the middle
                }
            }
            .then(chain.filter(exchange)
            .doFirst {
                hub.configureScope { scope ->
                   //something change on first
                }
            }
            .doFinally {
               hub.configureScope { scope -> 
                  //something change on finally
               }
            }
    }
}