With Fedora 26 I had sporadic problems with the system crashing at the first
kernel mode switch, before entering the LUKS passphrase at boot time, but I
could hit reset and usually the second time it would work. With Fedora 27 this
happens to me consistently every time. The only way I can successfully boot is
to use "nomodeset" on the kernel command line, which then causes issues for my
X session.

My system has Asus Sabertooth 990FX R2.0 motherboard, AMD FX-8350 CPU, and
Radeon HD 5850 graphics card. I'm running Fedora 27 with kernel
4.15.3-300.fc27.x86_64.

Fedora Bugzilla shows someone else having that problem with HD 5450. Maybe its
a general Evergreen problem.

https://bugzilla.redhat.com/show_bug.cgi?id=1474044