Hello. I think I may have the same problem - but the thread is long and I have not assimilated all of it. My problem is that LibreOffice Impress causes a really hard hang when using an HDMI external monitor. (I reported that problem here on this board. I have worked around the problem with a kernel boot switch.)
Cf. also this problem, different but again involved with external monitors, and apparently caused by interaction between the kernel (well, some versions of it) and the very latest AMD F13 BIOS (which I have yet to install).