try without concurrency

package.json

@@ -9,8 +9,8 @@
     "build:dev:prod": "jlpm run integrity && jlpm run build:packages && jlpm run build:themes && cd dev_mode && jlpm run build:prod",
     "build:examples": "lerna run build --scope \"@jupyterlab/example-*\"",
     "build:packages": "cd packages/metapackage && jlpm run build",
-    "build:src": "lerna run build --scope \"@jupyterlab/!(test-|example-)*\"",
-    "build:test": "lerna run build --scope \"@jupyterlab/test-*\"",
+    "build:src": "lerna run build --scope \"@jupyterlab/!(test-|example-)*\" --concurrency 1",
+    "build:test": "jlpm run build:testutils && lerna run build:test && lerna run build --scope \"@jupyterlab/test-*\" --concurrency 1",
     "build:testutils": "cd testutils && jlpm run build",
     "build:themes": "node buildutils/lib/build-themes.js",
     "build:update": "jlpm run pre-publish && node buildutils/lib/update-core-mode.js",