The early return in G1HeapRegionManager::find_contiguous_allow_expand that checks whether we have enough regions to satisfy an allocation does not consider free regions:

  // Check if we can actually satisfy the allocation.
  if (num_regions > available()) {
    return G1_NO_HRM_INDEX;
  }
Therefore, a `expand_and_allocate_humongous` call may fail, even though a subsequent `expand_and_allocate` call succeeds. This can lead to unexpected allocation behavior.