It currently looks like the `map.get(element)` returns `undefined` even for previously-loaded elements. Are we evicting from the cache prematurely? Why?

Our second level caching (inside of `parseHookNames`) is working but this is still resulting in a lot of unnecessary work.
}
    if (__DEBUG__) {
      console.log(
        'findHookNames() mapped line number',
        lineNumber,
        'to',
        originalSourceLineNumber,
      );
    }
    if (originalSourceLineNumber === null) {
      return null;
    }
    const name = getHookName(
      hook,
      hookSourceData.originalSourceAST,
      ((hookSourceData.originalSourceCode: any): string),
      ((originalSourceLineNumber: any): number),
    );
    if (__DEBUG__) {
      console.log(`findHookNames() Found name "${name || '-'}"`);
    }
    map.set(hook, name);
  });
  return map;
}
function loadSourceFiles(
  locationKeyToHookSourceData: Map<string, HookSourceData>,
): Promise<*> {
  
  const fetchPromises = new Map();