Screen updates stop after a few seconds

[LRN]

Windows 10 x86_64, UltraVNC server 1.2.1.3 (or 1.2.1.2).
After connecting with a viewer, i see the remote desktop for a couple of seconds. Then updates stop. Asking for a refresh results in a black screen being shown. Input is still sent and received in both directions (viewer can move host cursor; viewer also sees when host cursor moves; viewer sees cursor changes when it hovers over different widgets), clicks work (though, obviously, viewer has no way to know, since nothing is shown). Sending CTRL+ALT+DEL brings up the CTRLALTDEL Windows 10 screen and resumes screen updates. Pressing Cancel dismisses the CTRLALTDEL screen, and updates stop after a couple of seconds.
I've tried tinkering with the Radeon options, disabling crossfire (the laptop in question has AMD APU and GPU, i.e. DualGraphics), that has no impact.
I've tried connecting via SSVnc viewer from a Debian machine - same result (updates stop, refresh turns the screen black; cursor and input work).

VNC used to work on the laptop in question, i suspect that Microsoft broke something.

[LRN]

Disabling AMD Radeon(TM) R7 Graphics device (the other is R5 M200) resumes the updates (with obvious side-effects of not having hardware-accelerated desktop).