Its the casette cog.

There is no way that the chain is coming off because of tension issues. That chain is tighter than my fixed gear bikes and my s/s mtb. Get a s/s specific cog. You have a combo that is designed to make shifting gears easier, and with heavy torque and even slightly off chainline, off comes the chain. S/s cogs have higher/pointier teeth to engage the chain. I use a ramped chainring on my bike with s/s cogs and it's never come off.

And out of curiosity, why 44-25? Thats a bizarre choice, less than 2-1 ratio. Are you doing massive climbs? I run 34-14 and 32-16 on mine ( two rings, two cogs). Smaller chainrings give more options as well for chainline adjustment. You can move the chainring to the inside of the spider and/or get a shorter b/b to straighten the chainline.