GHA cache has stopped working

[swails]

Contributing guidelines

• I've read the contributing guidelines and wholeheartedly agree

I've found a bug, and:

• The documentation does not mention anything about my problem
• There are no open or closed issues that are related to my problem

Description

Some of our workflows that have used GHA cache to speed builds have been failing recently. Here is the relevant part of the GHA workflow (reusable composite action):

    - name: Build docker image
      uses: docker/build-push-action@v6
      with:
        context: ${{ github.workspace }}/${{ inputs.working_directory }}
        file: ${{ github.workspace }}/${{ inputs.working_directory }}/${{ inputs.dockerfile }}
        push: true
        tags: ghcr.io/<org>/${{ inputs.image_name }}:${{ inputs.ref }}
        build-args: ${{ inputs.build-args }}
        secrets: ${{ inputs.secrets }}
        cache-from: type=gha
        cache-to: type=gha,mode=max

Here is the error message:

#14 exporting to GitHub Actions Cache
#14 preparing build cache for export
#14 preparing build cache for export 0.3s done
#14 ERROR: failed to parse error response 400: <h2>Our services aren't available right now</h2><p>We're working to restore all services as soon as possible. Please check back soon.</p>06d6yaQAAAABSQOSnwzVCQpS0QQaM/XovUEhMMzBFREdFMDEwOABFZGdl: invalid character '<' looking for beginning of value
------
 > importing cache manifest from gha:1344117493793766147:
------
------
 > exporting to GitHub Actions Cache:
------

 1 warning found (use --debug to expand):
 - UndefinedVar: Usage of undefined variable '$PYTHONPATH' (line 14)
ERROR: failed to solve: failed to parse error response 400: <h2>Our services aren't available right now</h2><p>We're working to restore all services as soon as possible. Please check back soon.</p>06d6yaQAAAABSQOSnwzVCQpS0QQaM/XovUEhMMzBFREdFMDEwOABFZGdl: invalid character '<' looking for beginning of value
Reference
Check build summary support
Error: buildx failed with: ERROR: failed to solve: failed to parse error response 400: <h2>Our services aren't available right now</h2><p>We're working to restore all services as soon as possible. Please check back soon.</p>06d6yaQAAAABSQOSnwzVCQpS0QQaM/XovUEhMMzBFREdFMDEwOABFZGdl: invalid character '<' looking for beginning of value

This has been going on for several days now with no reported outages from GitHub (despite what the response message says). I'm currently blocked from updating to v7 because of self-hosted runner dependency versions. The only thing that currently works is disabling the cache.

Expected behaviour

The image builds and pushes without failure

Actual behaviour

The build fails

Repository URL

No response

Workflow run URL

No response

YAML workflow

- name: Build docker image
      uses: docker/build-push-action@v6
      with:
        context: ${{ github.workspace }}/${{ inputs.working_directory }}
        file: ${{ github.workspace }}/${{ inputs.working_directory }}/${{ inputs.dockerfile }}
        push: true
        tags: ghcr.io/<org>/${{ inputs.image_name }}:${{ inputs.ref }}
        build-args: ${{ inputs.build-args }}
        secrets: ${{ inputs.secrets }}
        cache-from: type=gha
        cache-to: type=gha,mode=max

Workflow logs

#14 exporting to GitHub Actions Cache
#14 preparing build cache for export
#14 preparing build cache for export 0.3s done
#14 ERROR: failed to parse error response 400: <h2>Our services aren't available right now</h2><p>We're working to restore all services as soon as possible. Please check back soon.</p>06d6yaQAAAABSQOSnwzVCQpS0QQaM/XovUEhMMzBFREdFMDEwOABFZGdl: invalid character '<' looking for beginning of value
------
 > importing cache manifest from gha:1344117493793766147:
------
------
 > exporting to GitHub Actions Cache:
------

 1 warning found (use --debug to expand):
 - UndefinedVar: Usage of undefined variable '$PYTHONPATH' (line 14)
ERROR: failed to solve: failed to parse error response 400: <h2>Our services aren't available right now</h2><p>We're working to restore all services as soon as possible. Please check back soon.</p>06d6yaQAAAABSQOSnwzVCQpS0QQaM/XovUEhMMzBFREdFMDEwOABFZGdl: invalid character '<' looking for beginning of value
Reference
Check build summary support
Error: buildx failed with: ERROR: failed to solve: failed to parse error response 400: <h2>Our services aren't available right now</h2><p>We're working to restore all services as soon as possible. Please check back soon.</p>06d6yaQAAAABSQOSnwzVCQpS0QQaM/XovUEhMMzBFREdFMDEwOABFZGdl: invalid character '<' looking for beginning of value

BuildKit logs

Additional info

No response