My laptop with an AMD APU A10-5750M which is based on the Richland-architecture boots with a flashing cursors in the left corner. It boots fine with the nomodeset parameter. This is because that in the kernel parameters this is forced: radeon.si_support=0 radeon.cik_support=0 amdgpu.si_support=1 amdgpu.cik_support=1 This makes the OS try to use the AMDGPU drivers which is not supported for Richland. This has come in a new kernel update because it worked fine before. If i remove that line it boots fine but with a sudo clr-boot-manager they get back there. I have checked in /etc/kernel/cmdline.d and they are not there so i have not forced this myself.
I had this case too. In my case boot fails with black screen and flashing cursor only one time. Then when I forcefully shutdown my laptop and again start it then it works. I am on AMD Raedoen R5 Graphics Card.
I didn't but now i did so now I know how to fix this. However, should that really be there when it makes some computer won't boot with Solus? If it will remain there I think this should be added to the help center how to fix this if you have a computer that won't boot with that line.
It's not related to AMD in my case as I use an Intel® Core™ i5-2540M CPU @ 2.60GHz × 4. It happened for the first time as I was aborting an update in the software center (linux firmware and linux kernels) as it was too slow (around 50kb/s). I aborted the downloads during downloading stage, not updating stage though. I had to cold reboot and was able to get into Solus again.
So I've tried to modify this line radeon.si_support=0 radeon.cik_support=0 amdgpu.si_support=1 amdgpu.cik_support=1 to radeon.si_support=1 radeon.cik_support=1 amdgpu.si_support=1 amdgpu.cik_support=1 and now my laptop boots with the radeon driver and my desktop with a radeon 290 boots with the amdgpu driver so that solves the issue.