I'm running Raft from terminal. Lag is crazy in game and whole pc while game running even writing this.

My video card is not great but runs minetest and minecraft are fine for instance.

Does this give a clue?

$ ./V1.04_Raft_LinuxUniversal.x86_64 
Set current directory to ~/raft/V1.04_Raft_LinuxUniversal
Found path: ~/raft/V1.04_Raft_LinuxUniversal/V1.04_Raft_LinuxUniversal.x86_64
Mono path[0] = '~/raft/V1.04_Raft_LinuxUniversal/V1.04_Raft_LinuxUniversal_Data/Managed'
Mono path[1] = '~/raft/V1.04_Raft_LinuxUniversal/V1.04_Raft_LinuxUniversal_Data/Mono'
Mono config path = '~/raft/V1.04_Raft_LinuxUniversal/V1.04_Raft_LinuxUniversal_Data/Mono/etc'
displaymanager : xrandr version warning. 1.4
displaymanager : trying .X11-unix
client :0 has 1 screens
displaymanager screen (0): 1024 x 768
Using libudev for joystick management
Importing game controller configs

Thanks in advance.

EDIT

When Raft is allowed to load and Exit (almost unplayable) the trace above now shows final line:

Segmentation fault

Same behavior seen on another machine. Both are running Debian 8, Jessie. Tried different graphics permutations, as expected best is with graphics quality "Simple" and a resolution confirmed to be supported by xrandr. (Lower resolutions "Windowed" are a little less bad)

Not sure how to start debugging this but someone said i should try strace.

strace -o output.txt -e open ./V1.04_Raft_LinuxUniversal.x86_64 

I took that output and in this link show lines with "Error No Entry"

https://pastebin.com/jLQ23zBN