ERR_CONTENT_DECODING_FAILED for WebGL Brotli-compressed .data.br when patched with USSR v1.1.8

[scozirge]

Version

• USSR-v1.1.8-net6.0-win-x64.zip
• Unity 2022.3.46f1

Environment

• Browser: Chrome (latest)
• Hosting: Google Cloud Storage (using gsutil setmeta to set Content-Encoding: br and correct Content-Type headers)

Steps to reproduce

1. In Unity, enable Publishing Settings → Compression Format → Brotli and build a WebGL project.
2. Locate the generated Build_WebGL.data.br.
3. Run USSR, choose Remove Unity Splash Screen, and select that .data.br file.
4. USSR creates a backup and patches the .data.br in place.
5. Upload the entire Build/ folder to GCS
6. Open index.html in Chrome.

Actual result

• Chrome fails to load the patched file and reports:

The Error Shows Below:

GET https://xxxxxxxxx/xxxxxxxxxx/Build/acc473b6569bcfad667f680b1f9092b0.data.br net::ERR_CONTENT_DECODING_FAILED 200 (OK)
u @ bb0d9ecdb05db3e84da20bd14a4f84dc.loader.js:1
(anonymous) @ bb0d9ecdb05db3e84da20bd14a4f84dc.loader.js:1
Promise.then
l.cachedFetch @ bb0d9ecdb05db3e84da20bd14a4f84dc.loader.js:1
T @ bb0d9ecdb05db3e84da20bd14a4f84dc.loader.js:1
(anonymous) @ bb0d9ecdb05db3e84da20bd14a4f84dc.loader.js:1
createUnityInstance @ bb0d9ecdb05db3e84da20bd14a4f84dc.loader.js:1
script.onload @ index.html:107
script
(anonymous) @ index.html:104Understand this error
bb0d9ecdb05db3e84da20bd14a4f84dc.loader.js:1 [UnityCache] Failed to load 'https://xxxxxxxx/xxxxxxx/Build/acc473b6569bcfad667f680b1f9092b0.data.br' from indexedDB cache due to the error: TypeError: network error
bb0d9ecdb05db3e84da20bd14a4f84dc.loader.js:1

GET https://xxxxxxxxx/xxxxxx/Build/acc473b6569bcfad667f680b1f9092b0.data.br net::ERR_CONTENT_DECODING_FAILED 200 (OK)
l.fetchWithProgress @ bb0d9ecdb05db3e84da20bd14a4f84dc.loader.js:1
(anonymous) @ bb0d9ecdb05db3e84da20bd14a4f84dc.loader.js:1
Promise.catch
l.cachedFetch @ bb0d9ecdb05db3e84da20bd14a4f84dc.loader.js:1
T @ bb0d9ecdb05db3e84da20bd14a4f84dc.loader.js:1
(anonymous) @ bb0d9ecdb05db3e84da20bd14a4f84dc.loader.js:1
createUnityInstance @ bb0d9ecdb05db3e84da20bd14a4f84dc.loader.js:1
script.onload @ index.html:107
script
(anonymous) @ index.html:104Understand this error
bb0d9ecdb05db3e84da20bd14a4f84dc.loader.js:1 Failed to download file Build/acc473b6569bcfad667f680b1f9092b0.data.br
(anonymous) @ bb0d9ecdb05db3e84da20bd14a4f84dc.loader.js:1
Promise.catch
T @ bb0d9ecdb05db3e84da20bd14a4f84dc.loader.js:1
(anonymous) @ bb0d9ecdb05db3e84da20bd14a4f84dc.loader.js:1
createUnityInstance @ bb0d9ecdb05db3e84da20bd14a4f84dc.loader.js:1
script.onload @ index.html:107
script
(anonymous) @ index.html:104Understand this error
a4d522e9144b721a40631eec1f74db9b.framework.js.br:10 navigator.mediaDevices support available
bb0d9ecdb05db3e84da20bd14a4f84dc.loader.js:1 Uncaught (in promise) TypeError: Cannot read properties of undefined (reading 'buffer')
at bb0d9ecdb05db3e84da20bd14a4f84dc.loader.js:1:8941

Additional Notes:
If I disable Brotli compression in Unity and patch the uncompressed *.data file, then manually re-compress with brotli --best, the file loads correctly.