Running Beta 1 on my 2014 Macbook Pro. I could not mount the SD card from my camera, when placing it in the slot. The Apple System Report did not even see the device.
The workaround was/is to already have the card in the slot when booting the machine. Then the device is recognized, the card mounts and the import to Photos proceeds nominally. However, unmounting and removing the card sets the machine back to square one, so the procedure has to be repeated if one wants to use a different card.
Is anyone else seeing this, or have a different workaround? In any case, to quote SpaceX, this is why we test. :-)