This happened to me 7 days ago when Fedora replaced kernel-4.18.18-300.fc29
with kernel-4.19.2-300.fc29.  Also on kernel-4.19.3-300.fc29 from yesterday. 
 On a different hard drive I tried rawhide and kernel-4.20.0-0.rc3.git1.1.fc30.
 Same thing.  I have also been using radeon.cik_support=0 amdgpu.cik_support=1
amdgpu.dpm=1 amdgpu.dc=1 because it crashes without it.  Removing amdgpu.dpm=1
didn't fix this.  Removing all of these didn't fix this.  I have a Sapphire R9
290.  Fedora says downgrading the kernel isn't supported but downgrading to
kernel-4.18.18-300.fc29 seems to work.