I just deployed two ASRock DeskMini mini-STX mini PCs, connected to my two 40" 4K UHD TVs. Both of them are connected via native HDMI 1.4, both of them are running the HD 510 iGPU. (One CPU is a G3900, one is a G4400.) Both are running Win10 Pro 1607 64-bit with newest updates.
I haven't tried waking up the other one, but this one, with the G4400, has the same problem as the OP. When I wake it, all of the windows, are all scrunched up in the upper-left corner, like a 1024x768 screen or so.
Note that it doesn't do that right when the monitor goes into monitor-save mode, if I wake it up immediately after that happens, then there's no issue. Only when I leave it for a while. (Monitor actually switches off?)