Hmm ... can you check if it really loaded the new kernel and not the old 4G one?  Because here on test system (Linux, 19.30 driver & Windows 10, Adrenalin 19.30) the V56 is at ~1.04 g/s. What I could imagine is that if you run an older driver or ROCm then the load of the binary kernal fails and it falls back to the backup 4G solver.

Here what the testsys (2x 56, 1x 64 in the middle, optimized clocks for performance/watts) just produced:

Edit:
In case its ROCm: will provide ROCm builds in next version