Check the manometer soapy water. If bubbles appear then degass (shoot all the air to zero pressure or SLOWLY! loosen the mamometer till you hear a slight hiss then STOP!!! let all the air piss out) unscrew the manometer and wrap Teflon tape on the threads and screw it back in. Its probably the mamometer.
Could also possibly be the hammer spring is too maxed out maybe...
Another possibility is the check valve isn't sealed and maybe dust or debris got inside. I would use a tank to blast couple short deliberate bursts of air to attempt to dislodge any dust and debris to prevent the check valve seal from closing all the way.
If you can't do it without being extra careful as to not make it noticeable that you tampered with it then just send it in for warranty or refund.
If the leak isn't that bad you could just fill it only when you are ready to go shooting and always store it low on air right below the yellow where the leak stops.
I would fill it, then remove the air tube, if it doesn't leak it's the hammer spring. You can also put a balloon on both ends of the cylinder to see if they inflate. Hatsan flash are easy to work on, I have 2.
Thank you for all the help. I will send it back to the factory for warranty repairs after i check gauge for leaks. The hammer spring has not been adjusted.