Comment # 8 on bug 89059 from Sebastian Parborg

This might not be related at all, but are you using "xf86-video-ati" for mode
setting or the "modesetting" driver that comes with Xorg?

I switched to the modesetting one because I saw that you could gain a couple
fps when doing so. I got a few more fps (1-8fps) in the games I tried. But when
I try to play Dota2 it hard locks after a while. The computer doesn't freeze
but I have to manually kill dota2.

When switching back to video-ati, I haven't gotten any of these hard locks yet.
Perhaps they are unrelated, or the same thing that managed to hardlock Dota2
with the "modesetting" driver is doing the same thing to you.