Workaround for issue https://github.com/playframework/playframework/issues/7056 and https://github.com/playframework/play-ws/issues/87 . Copy the ahc-default.properties file into your conf/ folder

ahc-default.properties

play.shaded.ahc.org.asynchttpclient.threadPoolName=AsyncHttpClient
play.shaded.ahc.org.asynchttpclient.maxConnections=-1
play.shaded.ahc.org.asynchttpclient.maxConnectionsPerHost=-1
play.shaded.ahc.org.asynchttpclient.connectTimeout=5000
play.shaded.ahc.org.asynchttpclient.pooledConnectionIdleTimeout=60000
play.shaded.ahc.org.asynchttpclient.connectionPoolCleanerPeriod=1000
play.shaded.ahc.org.asynchttpclient.readTimeout=60000
play.shaded.ahc.org.asynchttpclient.requestTimeout=60000
play.shaded.ahc.org.asynchttpclient.connectionTtl=-1
play.shaded.ahc.org.asynchttpclient.followRedirect=false
play.shaded.ahc.org.asynchttpclient.maxRedirects=5
play.shaded.ahc.org.asynchttpclient.compressionEnforced=false
play.shaded.ahc.org.asynchttpclient.userAgent=AHC/2.0
play.shaded.ahc.org.asynchttpclient.enabledProtocols=TLSv1.2, TLSv1.1, TLSv1
play.shaded.ahc.org.asynchttpclient.enabledCipherSuites=TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384,TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256,TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256,TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA,TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA,TLS_RSA_WITH_AES_128_GCM_SHA256,TLS_RSA_WITH_AES_128_CBC_SHA,TLS_RSA_WITH_AES_256_CBC_SHA
play.shaded.ahc.org.asynchttpclient.useProxySelector=false
play.shaded.ahc.org.asynchttpclient.useProxyProperties=false
play.shaded.ahc.org.asynchttpclient.validateResponseHeaders=true
play.shaded.ahc.org.asynchttpclient.strict302Handling=false
play.shaded.ahc.org.asynchttpclient.keepAlive=true
play.shaded.ahc.org.asynchttpclient.maxRequestRetry=5
play.shaded.ahc.org.asynchttpclient.disableUrlEncodingForBoundRequests=false
play.shaded.ahc.org.asynchttpclient.removeQueryParamOnRedirect=true
play.shaded.ahc.org.asynchttpclient.useOpenSsl=false
play.shaded.ahc.org.asynchttpclient.acceptAnyCertificate=false
play.shaded.ahc.org.asynchttpclient.sslSessionCacheSize=0
play.shaded.ahc.org.asynchttpclient.sslSessionTimeout=0
play.shaded.ahc.org.asynchttpclient.tcpNoDelay=true
play.shaded.ahc.org.asynchttpclient.soReuseAddress=false
play.shaded.ahc.org.asynchttpclient.soLinger=-1
play.shaded.ahc.org.asynchttpclient.soSndBuf=-1
play.shaded.ahc.org.asynchttpclient.soRcvBuf=-1
play.shaded.ahc.org.asynchttpclient.httpClientCodecMaxInitialLineLength=4096
play.shaded.ahc.org.asynchttpclient.httpClientCodecMaxHeaderSize=8192
play.shaded.ahc.org.asynchttpclient.httpClientCodecMaxChunkSize=8192
play.shaded.ahc.org.asynchttpclient.disableZeroCopy=false
play.shaded.ahc.org.asynchttpclient.handshakeTimeout=10000
play.shaded.ahc.org.asynchttpclient.chunkedFileChunkSize=8192
play.shaded.ahc.org.asynchttpclient.webSocketMaxBufferSize=128000000
play.shaded.ahc.org.asynchttpclient.webSocketMaxFrameSize=10240
play.shaded.ahc.org.asynchttpclient.keepEncodingHeader=false
play.shaded.ahc.org.asynchttpclient.shutdownQuietPeriod=2000
play.shaded.ahc.org.asynchttpclient.shutdownTimeout=15000
play.shaded.ahc.org.asynchttpclient.useNativeTransport=false
play.shaded.ahc.org.asynchttpclient.ioThreadsCount=0

org.asynchttpclient.threadPoolName=AsyncHttpClient
org.asynchttpclient.maxConnections=-1
org.asynchttpclient.maxConnectionsPerHost=-1
org.asynchttpclient.connectTimeout=5000
org.asynchttpclient.pooledConnectionIdleTimeout=60000
org.asynchttpclient.connectionPoolCleanerPeriod=1000
org.asynchttpclient.readTimeout=60000
org.asynchttpclient.requestTimeout=60000
org.asynchttpclient.connectionTtl=-1
org.asynchttpclient.followRedirect=false
org.asynchttpclient.maxRedirects=5
org.asynchttpclient.compressionEnforced=false
org.asynchttpclient.userAgent=AHC/2.0
org.asynchttpclient.enabledProtocols=TLSv1.2, TLSv1.1, TLSv1
org.asynchttpclient.useProxySelector=false
org.asynchttpclient.useProxyProperties=false
org.asynchttpclient.validateResponseHeaders=true
org.asynchttpclient.strict302Handling=false
org.asynchttpclient.keepAlive=true
org.asynchttpclient.maxRequestRetry=5
org.asynchttpclient.disableUrlEncodingForBoundRequests=false
org.asynchttpclient.removeQueryParamOnRedirect=true
org.asynchttpclient.useOpenSsl=false
org.asynchttpclient.acceptAnyCertificate=false
org.asynchttpclient.sslSessionCacheSize=0
org.asynchttpclient.sslSessionTimeout=0
org.asynchttpclient.tcpNoDelay=true
org.asynchttpclient.soReuseAddress=false
org.asynchttpclient.soLinger=-1
org.asynchttpclient.soSndBuf=-1
org.asynchttpclient.soRcvBuf=-1
org.asynchttpclient.httpClientCodecMaxInitialLineLength=4096
org.asynchttpclient.httpClientCodecMaxHeaderSize=8192
org.asynchttpclient.httpClientCodecMaxChunkSize=8192
org.asynchttpclient.disableZeroCopy=false
org.asynchttpclient.handshakeTimeout=10000
org.asynchttpclient.chunkedFileChunkSize=8192
org.asynchttpclient.webSocketMaxBufferSize=128000000
org.asynchttpclient.webSocketMaxFrameSize=10240
org.asynchttpclient.keepEncodingHeader=false
org.asynchttpclient.shutdownQuietPeriod=2000
org.asynchttpclient.shutdownTimeout=15000
org.asynchttpclient.useNativeTransport=false
org.asynchttpclient.usePooledMemory=true

@Correction: copy those lines into a new file called ahc.properties inside /conf folder. ahc.properties is supposed to be where you put your custom async http client properties however it works as a workaround for this issue.