Separate sound from game readiness
A successful offline launch establishes that the playable game files are available. Sound has an additional requirement: the browser must be able to decode an available audio format. ORBIT tries another format when decoding the first one fails, but that fallback may require a network request.
The current build caches its WebM audio files and audio manifest. It deliberately leaves AAC fallback files out of the offline shell. That means offline audio is a capability to verify on your device, not something the general offline-ready message can guarantee for every browser.
Make the test specific
Open the game online and interact with it to start audio. Check Music and Sounds separately so you know which layers you expect to hear. Then finish the attempt, disconnect and reopen the same game context.
Interact again and listen for both the background audio and an action effect during a short run. If one is absent, record that distinction. A muted music preference, a silent effect and a complete failure of audio decoding have different symptoms even though each may initially be described as no sound.
Choose a useful fallback
If the forest plays but sound does not, you can still play silently. When connectivity returns, repeat the sound test online. Audio that returns only online is useful evidence of a missing or unsupported cached audio path, though output settings should still be checked.
Do not delete progress to troubleshoot sound. First check the in-game switches, device media volume and chosen audio output. If you report the issue, include browser, device, whether gameplay worked offline and whether music, effects or both were missing.