Exit code 01 can be caused by following.

0x00000001 – UNABLE_TO_INIT_DXGI
The game is unable to initialize a graphical subsystem. Possible solutions:

Update the graphics card drivers to a newer version.
Rollback the graphics card drivers to an older version.
Check the temperature of your GPUs and CPUs.
Disable the Steam Overlay.

Steam overlay and temps aren't the issue. My drivers are up-to-date so rolling back is the only one that could help.

Try also removing these startup parameters

-exThreads=7 -maxVRAM=3500 -maxMem=8961 -enableHT

350.12 drivers have the same issue so it isn't that.

I removed those parameters and still the same thing.

Workaround solutions for this are launching in windowed mode or clicking the Arma 3 logo on start up when it's loading addons and that stuff. Just need to be careful with the "Arma 3 is not responding" pop-ups that are caused by the clicking because you can quickly accidentally click the close program button. That's why it's likely some kind of a windows focus issue.

EDIT:

Launching windowed is the only workaround.

The DXGI seems to happen likely because I've to close the task from the task manager. I'm now trying to see if it's Avast doing something though I can likely say sure about that only in the next week. No time to test more.

RTSS RivaTuner Statistics Server seems to be the cause of this now. It wasn't back in the day when I reported because this happened even without it. Now this only happens if I've RTSS running.