I don't see any Centos drivers for your GPU. I think there are no Centos drivers compatible with your GPU. And your problem is exactly because of it
Radeon™ R7 300, R9 295X2, R9 280X, R9 280, R9 270X, R9 270, R7 265, R7 250X, R7 250, R7 240, HD 8500 - HD 8900, and HD 7700 – HD 7900 Series
I don't know if you could solve your problem already, but I had this same issue with Crimson 15.12 on Scientific Linux 7.3, it worked fine since 7.1 but with that last update I had troubles. I have an APU R7 250 and then I noticed that AMD had updated the drivers and now my system uses AMDGPU-PRO I installed it and worked everything fine. Sadly your GPU still uses Crimson on this page Linux Download Center but keep an eye on it, because I think the drivers for my system were updated just this week so hopefully you can get yours soon.
Alternatively if you still use Centos 7.2 or lower, what I did before was not to use the RHEL rpm, but download the generic Linux driver, run it and generate the rpm with it, I'm not sure if that's what you did but that helped be in the past.