I can confirm the same issue is happening with my Vega56 and happened before on my R9 Fury as well.
I keep reporting it to AMD, reported it to EA/Dice as well, but I suspect this is an issue with AMD's drivers especially if affects more games.
Made a graphics comparision between GTX 970 and RX Vega, the results clearly show downgraded terrain quality on the AMD card: https://imgsli.com/MzM0OQ