Running two ng serve instances (same project, different configurations) causes “504 Outdated Optimize Dep” errors in Angular CLI 20.3.8

Inizia con la riproduzione tramite package.json start:both e ispeziona la directory condivisa dell’ottimizzatore .angular/cache/.../vite mentre sono in esecuzione entrambi i processi ng serve. La correzione è completa quando i server paralleli per configurazioni diverse si caricano correttamente senza errori 504 Outdated Optimize Dep.

Command

serve

Is this a regression?

• Yes, this behavior used to work in the previous version

The previous version in which this bug was not present was

20.3.6

Description

Since updating to Angular v20.3.9 / CLI v20.3.8, it’s no longer possible to run two ng serve instances for the same project (e.g. localized builds) in parallel.
The second instance fails to load with a 504 (Outdated Optimize Dep) error for one or more chunks (e.g. chunk-5V7QYGNA.js).

This setup worked correctly in previous Angular 20.3.6 versions (before the CLI migrated the dev-server to the Vite-based implementation).

The issue appears to be caused by both ng serve processes sharing the same Vite optimizer cache directory inside .angular/cache/.../vite.
When one process updates or invalidates the cache, the other process detects stale metadata and refuses to serve pre-bundled chunks.

Minimal Reproduction

package.json scripts
"scripts": {
"start": "ng serve --host 0.0.0.0",
"startfr": "ng serve -c fr --host 0.0.0.0",
"startfr-alt": "ng serve -c fr --host 0.0.0.0 --port 4201",
"start:both": "concurrently "npm run start" "npm run startfr-alt""
}

Steps to reproduce
1. Run npm run start:both.
2. Wait for both dev servers to start.
3. Observe that the second instance fails to load in the browser console with:
Failed to load resource: the server responded with a status of 504 (Outdated Optimize Dep)

Exception or Error

Failed to load resource: the server responded with a status of 504 (Outdated Optimize Dep)

Your Environment

Angular CLI: 20.3.8
Node: 24.1.0
Package Manager: yarn 4.9.2
OS: darwin arm64
    

Angular: 20.3.9
... animations, common, compiler, compiler-cli, core, forms
... language-service, localize, platform-browser
... platform-browser-dynamic, router

Package                         Version
---------------------------------------
@angular-devkit/architect       0.2003.8
@angular-devkit/build-angular   20.3.8
@angular-devkit/core            20.3.8
@angular-devkit/schematics      20.3.8
@angular/cdk                    20.2.11
@angular/cli                    20.3.8
@angular/material               20.2.11
@schematics/angular             20.3.8
rxjs                            7.8.2
typescript                      5.8.3
zone.js                         0.15.1

Anything else relevant?

No response