Seem to be a driver issue as I'm having the same issues with my RX 480. I do have a working walk around.
1. Uninstall the current driver and AMD software from your computer.
2. Download update driver 17.2.1 from amd's driver website.
3. When prompted to install the 17.2.1 drivers. Click on "custom install" then UNCHECK all but the Display Driver and the Vulken Drivers. Do not install AMD settings as its causing 100% of my crashes. When u install, you should only be installing the display driver and vulken drivers only.
4. Depending on who makes your RX 480 (mine is sapphire) just download sapphire Trixx software and use that for OC and fan speeds. if its made by someone else, see if they have a OC tool app.
I hope this fixes it for you, it works for mine.