Operating system: Windows-10-10.0.18362-SP0 64 Bits
Graphics card: GeForce GTX 1060 6GB/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 431.70
Broken: version: 2.82 hash d35a31968707
Short description of error
Normal path tracing is unable to correctly preserve energy when two random walk SSS nodes are mixed, Branched Path Tracing meanwhile is able to keep said energy. The energy loss is greatest when the mix is at 0.5, diminishing to 0 when it's either one or the other. Something to note amid the talk of removing BPT altogether.
Exact steps for others to reproduce the error
Open the .blend file, set the view to 'rendered', switch from BPT to normal path tracing and notice the result becoming incorrect.