I'm seeing the same on a similarly spec test box. As noted, for now you can workaround the issue by opting out of the beta branch to use SteamVR 1.1.4. SteamVR 1.2.1 did not have this issue.
Tested with an RX 480 on Ubuntu 18.04.1 + SteamVR Experimental Graphics PPA and Gentoo with 18.3.1/7.0.1 and mesa git + llvm svn.
Disabling async reprojection avoids this issue.
Same issue here as well. Looks like something is borked on AMD hardware at the moment.
Tested on Ubuntu 18.04 + SteamVR Experimental Graphics PPA with RX Vega 64.
Downgraded to 1.1.4 for the time being as that mode still works fine.
Appears to be fixed in SteamVR beta 1.2.5, displays normally and says "Reprojection On" in the settings.
Nothing extracted yet.
Your system information
Please describe your issue in as much detail as possible:
With the recent update to SteamVR beta 1.2.3, my Vive only displays white. The display-mirror shows the image correctly and previous versions (stable, rolled-back beta) appear to display fine on the HMD.
Steps for reproducing this issue: