sbtからnpm startを起動してもlocalhost:3000にアクセスできない

scala-playframeworkを利用して、フロント側をreactで構築するwebアプリを開発しようとしています。
構築手法は参考サイトを追ってみてブラウザが立ち上がるところまではいったのですが、(sbtでplay側：localhost:9000とreact側：localhost:3000をsbt runで同時に立ち上げるもの)localhost:3000へのアクセスができない状態です。

ディレクトリ構造

myproject（sbtプロジェクト）
｜＿＿app
｜＿＿conf
｜...
｜＿＿ui (フロント側のソース)
｜　　｜＿＿public
｜　　｜＿＿src
｜　　｜＿＿package.json
｜　　｜...

実行結果

IntelliJからsbtで実行

bash
1C:\Users\yay\myproject>sbt run
2[info] welcome to sbt 1.3.13 (Oracle Corporation Java 11.0.2)
3[info] loading global plugins from C:\Users\yay.sbt\1.0\plugins
4...
5--- (Running the application, auto-reloading is enabled) ---
6[info] p.c.s.AkkaHttpServer - Listening for HTTP on /0:0:0:0:0:0:0:0:9000
7(Server started, use Enter to stop and go back to the console...)
8> ui@0.1.0 start C:\Users\yay\myproject\ui
9> react-scripts start
10i ・｢wds・｣: Project is running at http://xxx.xxx.xxx.xxx/
11i ・｢wds・｣: webpack output is served from
12i ・｢wds・｣: Content not from webpack is served from C:\Users\yay\myproject\ui\public
13i ・｢wds・｣: 404s will fallback to /
14Starting the development server...
15WARNING: An illegal reflective access operation has occurred
16WARNING: Illegal reflective access by com.google.inject.internal.cglib.core.$ReflectUtils$1 (file:/C:/Users/yay/AppData/Local/Coursier/cache
17/v1/https/repo1.maven.org/maven2/com/google/inject/guice/4.2.3/guice-4.2.3.jar) to method java.lang.ClassLoader.defineClass(java.lang.String,b
18yte[],int,int,java.security.ProtectionDomain)
19WARNING: Please consider reporting this to the maintainers of com.google.inject.internal.cglib.core.$ReflectUtils$1
20WARNING: Use --illegal-access=warn to enable warnings of further illegal reflective access operations
21WARNING: All illegal access operations will be denied in a future release
222020-09-28 03:04:32 INFO play.api.http.EnabledFilters Enabled Filters (see <https://www.playframework.com/documentation/latest/Filters>):
23   play.filters.csrf.CSRFFilter
24   play.filters.headers.SecurityHeadersFilter
25   play.filters.hosts.AllowedHostsFilter
262020-09-28 03:04:32 INFO play.api.Play Application started (Dev) (no global state)

uiディレクトリ内でnpm startをすれば普通にlocalhostにアクセスできます。

bash
1C:\Users\yay\myproject\ui>npm start
2> ui@0.1.0 start C:\Users\yay\myproject\ui
3> react-scripts start
4i ・｢wds・｣: Project is running at http://192.168.2.100/
5i ・｢wds・｣: Project is running at http://xxx.xxx.xxx.xxx/
6i ・｢wds・｣: webpack output is served from
7i ・｢wds・｣: Content not from webpack is served from C:\Users\yay\myproject\ui\public
8i ・｢wds・｣: 404s will fallback to /
9Starting the development server...
10Files successfully emitted, waiting for typecheck results...