I've been using a FirePro W4100 with a projector with DisplayPort 1.1a inputs for years, and it works without any issues. I upgraded to a Radeon Pro WX 7100, and now the projector output is glitching. After much troubleshooting it seems the DisplayPort link bit rate is getting set to 1.62Gbit/s on the WX 7100, suggesting that it is falling back to RBR speed, whereas the FirePro 4100 reports a 2.7 Gbit/s link speed, indicating it's running in HBR mode. It appears the link training is failing. I also tested with an old W8100 I had around and it worked like the W4100.
Is there a way to force the DisplayPort outputs into HBR mode? Or has anyone else seen this?