I'm using Vega 56 in my eGPU solution (HP Omen Accelerator paired with Intel Skull Canyon) and I saw that GPU-Z/AIDA64/AMD Control Panel and basically any other aplication report that card is working with 16x speed which is impossible due to TB3 limit.
My previous cards (R9 290 and GTX1070Ti) reported link speed correctly at 4x.
I observed this issue on few drivers versions back to 2017 and two Windows 10 build (1709 and 1809).
It's a cosmetic issue because my GPU working perfectly fine and AIDA64 bandwith test (GPGPU test shows typical bandwith for TB3).
I didn't saw any issues with that, I'm just reporting it because I never saw such an bug/bad info with other GPUs.