Mmmm. Sounds like your damper is slowly loosing fluid (into the lowers). This can appear intermittent with the pumping up and down ideas above cure it (temporarily). The test is if you can loosen off the bottom bolt on the lowers damper side) and see if blue fluid comes out. If youve got a rebound adjuster there it may need a stiff tug to get it off. If it's all brown fluid you can just put it back in – make sure the fluid is super clean!
If blue fluid – the damper is leaking. The ideal solution is a full service / warranty return but you can get around it by draining the lowers and topping up the damper by the same amount -10ml (and putting the 10 ml correct fluid in the lowers). But never never ever overfill the damper.
btw – dont ignore it. The side effect of extra fluid in the lowers is that your total travel is significantly reduced. The spring side is meant to do all the susp work but with a reduced volume in your lowers means the fork cant get to its max travel.