It's definitely a bug. I disabled 4G Decoding, BAR in the BIOS, rebooted, DDU'd the drivers, reinstalled drivers, tested without Smart Access Memory, then tested again with it back on and now back to 1 GPU still.
Looking to see if something else I was doing caused it to pop two instances of the miner. The limited time I was running, it was in fact getting 80mh at the pool and had both compute 0 and compute 1 under load in the GPU monitor; now I just get compute 0 with the single thread.
Bottom line, bug or not, there is headroom here for dev to enable that second thread officially.
Never thought that is possible to miner recognize 2 GPUs like this, it makes no sense

But now, with miner recognizing only one GPU, what's the hasrate? 62 to 65mhs as in your first video?
And maybe you found a bug and devs could use this approach to modify how miner works, at least with new AMDs cards