I've installed drivers from
https://launchpad.net/~oibaf/+archive/ubuntu/graphics-drivers to make sure, they are up to date.
Also, here are the logs from console, if they are of any help:
00:00:14.29 [INFO ] sdl::window_manager : platform - Linux
00:00:14.29 [INFO ] sdl::window_manager : video driver - x11
00:00:14.29 [INFO ] sdl::window_manager : display - 0
00:00:14.29 [INFO ] sdl::window_manager : number of displays 2
00:00:14.29 [INFO ] sdl::window_manager : number of drivers 2
00:00:14.29 [CRITICAL] Video mode set failed: Installed Vulkan doesn't implement the VK_KHR_surface extension
00:00:14.29 [INFO ] Joystick count : 0
00:00:14.29 [NOTICE ] Creating resource manager...
00:00:14.29 [DEBUG ] ./jh() [0x69fa13]
00:00:14.29 [DEBUG ] /lib/x86_64-linux-gnu/libc.so.6(+0x3ef20) [0x7fb1293f5f20]
00:00:14.29 [DEBUG ] ./jh() [0x603cf0]
00:00:14.29 [DEBUG ] ./jh() [0x5834cb]
00:00:14.29 [DEBUG ] ./jh() [0x5753fd]
00:00:14.29 [DEBUG ] ./jh() [0x498566]
00:00:14.29 [DEBUG ] ./jh() [0x4cafd7]
00:00:14.29 [DEBUG ] /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xe7) [0x7fb1293d8b97]
00:00:14.29 [DEBUG ] ./jh() [0x402a19]
00:00:14.29 [CRITICAL] Game has crashed! Please send this crash report to chaosforge team
Anyway, I've killed the summoner on MEDIUM for the first time - game is great!