Docker caching on GitHub Actions - `npm install` is not cached

Question

I am using the documented examples for caching Docker build layers via the GitHub Actions cache described here.

It appears to be working mostly as intended. It does successfully create a cache - and seems to pull many layers from it - but it does not cache arguably the most important layer: npm-modules

No changes to the dependency files are occurring during/prior to the builds below. Theoretically, these layers should be 100% reusable unless we make changes to the package.json - and it would save my build time ~1.5min

My setup in the workflow:

      - name: Setup Docker `buildx`
        uses: docker/setup-buildx-action@v2

      - name: Build & Push Docker Image 
        uses: docker/build-push-action@v4
        with:
          context: .
          file: Dockerfile.development
          push: true
          tags: |
            ${{ steps.docker-tags.outputs.tag }}
          cache-from: type=gha
          cache-to: type=gha,mode=max

Relevant stage of the Dockerfile:

# ------------------------------------------------------------------------------------------
# LAYER 2: Install dependencies only when needed
FROM base AS deps

# Check https://github.com/nodejs/docker-node/tree/b4117f9333da4138b03a546ec926ef50a31506c3#nodealpine to understand why libc6-compat might be needed.
RUN apk add --no-cache libc6-compat

# Create app directory
WORKDIR /usr/src/app

# Copy in dependency files
COPY .env.test .npmrc ./
COPY package.json package-lock.json ./

# Install production dependencies only
RUN npm ci --omit dev

Some steps are caching, from logs e.g.:

#8 [deps 1/5] RUN apk add --no-cache libc6-compat
#8 CACHED

#9 [deps 2/5] WORKDIR /usr/src/app
#9 CACHED

#10 [deps 3/5] COPY .env.test .npmrc ./
#10 CACHED

However, the next steps fail to cache:

#11 [deps 4/5] COPY package.json package-lock.json ./
# .....blahblahblah
#11 sha256:bc7465dc4da3894941da9beb13e53fea672b4167e0031a049feea4cd6ed2cd79 40.11MB / 40.11MB 1.1s done
#11 DONE 2.2s

#....more regarding copying in the package.json....

#12 [deps 5/5] RUN npm ci --omit dev
#12 23.50 npm WARN deprecated @babel/[email protected]: This proposal has been merged to the ECMAScript standard and thus this plugin is no longer maintained. Please use @babel/plugin-transform-class-properties instead.
#....blahblahblah
#12 75.77 added 1929 packages, and audited 1930 packages in 1m
#....blahblahblah
#12 DONE 76.9s

Weirdly, later in the Dockerfile I reference these modules:

# ------------------------------------------------------------------------------------------
# LAYER 3: Rebuild the source code only when needed
FROM node:18-alpine AS builder
WORKDIR /usr/src/app
COPY --from=deps /usr/src/app/node_modules ./node_modules

...which pulls from the cache, apparently.

#14 [builder 3/6] COPY --from=deps /usr/src/app/node_modules ./node_modules
#14 CACHED