Yep check the position of the poppet valve. Should stick out about 1mm from the air valve. See
https://m.pinkbike.com/u/scar4me/blog/manitou-mattoc-air-spring-issues.html
These forks need carful filling…. Bike upside down. Connect pump. Release all the air. Then pull up to extend to full travel. Then depress the valve again to purge any air left. Hold fully extended then pump up to desired pressure. Ensure you pull again maximising extension before you remove the pump.
One way to tell that the poppet valve is set correctly is to connect pump and cycle fork… Should feel soft. Push down half way and remove pump. If the fork stays in the same position the pos / neg Chambers are balanced. This shows poppet valve is ok. Connect pump, pull up on the leg and remove.
Don’t adjust air pressure with bike on the ground…. If you need more air… Completely empty and refill following the inverted procedure.
Does sound like the poppet has not fully closed leaving air to fill both Chambers (which results in virtually no resistance as you are finding)
Bit of a plop design but easy to fix with a spanner