Hi guys
I think you can safely move on to 18.20 & forget 18.10
it runs smoothly with Centos 7.5 & old prehistoric kernel 3.10.0-862.14.4.el7
after 4 days of troubleshooting the bloody amdgpu 18.20 driver, was able to update Centos 7.5 to the elrepo kernel 4.15.15
main problem was to BAN amdgpu driver to reach for not existing drm_backport.h file @ 4.x.x kernel system
this prehistoric drm_backport is used only in 3.10 kernel,
newer 4.x.x kernels does not support such a "fantastic" feature anymore
as soon as amdgpu-install script fails on 4.x.x kernel /it does however install almost all needed files 
/
with message: amdgpu dkms failed for running kernel
change the installed Makefile as follow:
sudo nano /usr/src/amdgpu-18.20-606296.el7/Makefile
comment out next line /aka add # at the beginning of line /
# -include /usr/src/kernels/$(KERNELRELEASE)/include/drm/drm_backport.h
save Makefile
run manual dkms
dkms remove -m amdgpu -v 18.20-606296.el7 --all
dkms add -m amdgpu -v 18.20-606296.el7 -k 4.15.15-1.el7.elrepo.x86_64
dkms build -m amdgpu -v 18.20-606296.el7 -k 4.15.15-1.el7.elrepo.x86_64
dkms install -m amdgpu -v 18.20-606296.el7 -k 4.15.15-1.el7.elrepo.x86_64
reboot
it should be now running with 14.15.15 kernel
some additional info:
elrepo kernel 4.17.x & 4.18.x was not working with amdgpu 18.20 due to: vga_switcheroo_set_dynamic_switch
/vga_switcheroo_set_dynamic_switch was implemented only up to 4.16 max, not higher/
elrepo kernel 4.16 was not working with amdgpu 18.20 either due to: amdgpu_connectors.c + drm_edid_to_eld
/amdgpu_connectors.c + drm_edid_to_eld was implemented only up to 4.15 max, not higher/
so I ended up running elrepo kernel 4.15.15 with amdgpu 18.20 driver, for the moment very happy with it
as I needed an up-to-date kernel as I have a great amd combo at home: ryzen 2600 & vega 56
