This is fixed in Divi 5. Or I should say, it’s no longer relevant and will no longer occur.
The builder is cached, which makes it load fast. However, when something changes, that cache needs to be cleared. When this happens, the spinner comes back to allow for the builder to load without its cached assets.
The double loading, which is actually an extended loading rather than a double loading, most commonly occurs when the cache gets invalidated for some reason. This should never happen normally, but some plugins inject dynamic data into the cached assets, which cause them to invalidate the cache on every page load.
In Divi 5, nothing is cached. It’s fast enough without caching.