2 Years and RX Vega 56 still doesn't have proper driver support. Some of the cards have an issue where the driver will crash every few minutes randomly even under no work load. I happen to own one of these cards. AMD released a driver that fixes this: Driver 17.11.3 which is less likely to crash but still crashes.
Articles covering this "Hotfix" Driver:
*This is not a PSU issue* I have a relatively new Evga 850 G3 and other people also had decent power supplies.
If anyone knows of a fix or has any recommendations I would be glad to hear them.
Other forums posts I've read suggested the issue was with the HBM2 memory clock speeds crashing, but I haven't investigated this myself yet. Also I did use DDU and so did other people, that doesn't solve the problem.
*edit* As an update the only driver so far that seems to be stable is 17.12.1 after going into wattman and selecting the "power save" profile.