Packaged app takes very long to start

I’m fairly new to Unreal development and starting to get the hang of it, but one issue that persists and I have no clue what is happening is the initial black screen when launching the packaged version of the app. On my beast of a machine, it’s just a couple seconds, but once uploaded to Furioos for streaming, it takes roughly 20 seconds, which is not ideal at all… Furioos have an Unreal demo project that immediately launches without black screen, and directly displays a loading screen.

The scene of the app is extremely small : a SunSky, ExponentialHeightFog, PostProcessVolume, FirstPersonCharacter and an empty Actor that loads a GLTF (with the glTFRuntime plugin) and does so quite fast once the initial load is complete.
What happens during this black screen ? What can I do to view some logs of what is happening ? And more importantly, how can I get rid of or reduce to a minimum this time ?