Also note that there is no launch parameters set

Update, been doing some troubleshooting myself.

Looks like DayZ is over-committing memory, it's hitting the DayZ hard limit of 2048MB and then leaking slowly.

If you set the steam launch option:

-maxMem=2047

You stop the game from hitting the DayZ limit and thus the process does not leak the memory.

Been running stable for 2 hours+ now.