We will draw 3 vertices as GL_TRIANGLES, so v1 will read three first FFF's from the buffer, n1 will read the first I's (at positions 3, 7, 11 starting from 0). v2 will read second three F's and n2 will read the second three I's.
Expected behavior: we should see a window with a smoothly colored triangle:
this is what we see on Nvidia or Intel hardware, and on AMD hardware (tested with RX550, Windows 10) with the driver version below 27.20.14501.
Observed behavior (with new 27.20.14501 driver):
i.e. all v2 and n2 vertices are sampled from the first vertex they should be sampled from. The problem is widespread: we got reports from various RX5**, R7 and R9 owners.