What's the relation between feelings of neither-pleasure-nor-pain and ignorance? I often see in some suttas that there are some habitual tendencies that, after the arising of pleasent feeling or painful feelings, lead to suffering due to passion for the pleasure and aversion for the pain.

But beside those two modes of feelings, there is a neutral kind of feeling, which neither-pleasent-nor-painful. In the suttas, such as MN 44 and MN 148, it is stated that neutral feeling accompanied with ignorance leads to suffering, because one does not see the gratification, the danger and the escape from suffering. 

I do understand the reasoning behind the two former modes of feelings and their relation with passion and aversion, but I can't grasp the idea behind neutral feelings and ignorance.

Can someone explain the influence of ignorance over neutral feelings and its connection with suffering?

Maybe some examples from the suttas or from everyday life might be helpful.

Thanks for your time and patience!
The definition of the 3 feelings come in MN 44 and their relationships to the 3 underlying tendencies towards greed, repulsion and ignorance:


  “Pleasant feeling is pleasant when it remains and painful when it
  perishes.
  “Sukhā kho, āvuso visākha, vedanā ṭhitisukhā vipariṇāmadukkhā;
  
  Painful feeling is painful when it remains and pleasant when it
  perishes.
  dukkhā vedanā ṭhitidukkhā vipariṇāmasukhā;
  
  Neutral feeling is pleasant when there is knowledge, and painful when
  there is ignorance.”
  adukkhamasukhā vedanā ñāṇasukhā aññāṇadukkhā”ti.
  
  “The underlying tendency for greed underlies pleasant feeling. The
  underlying tendency for repulsion underlies painful feeling. The
  underlying tendency for ignorance underlies neutral feeling.”
  “Sukhāya kho, āvuso visākha, vedanāya rāgānusayo anuseti, dukkhāya
  vedanāya paṭighānusayo anuseti, adukkhamasukhāya vedanāya avijjānusayo
  anusetī”ti.


In Contemplation of Feeling, Nyanaponika Thera explained this:


  Pleasant feeling is habitually linked with enjoyment and desire;
  unpleasant feeling with aversion; neutral feeling with boredom and
  confusion, but also serving as background for wrong views.


Also in SN 36.5:


  “Mendicants, there are these three feelings. What three? Pleasant,
  painful, and neutral feeling. Pleasant feeling should be seen as
  suffering. Painful feeling should be seen as a dart. Neutral feeling
  should be seen as impermanent. When a mendicant has seen these three
  feelings in this way, they’re called a mendicant who has cut off
  craving, untied the fetters, and by rightly comprehending conceit has
  made an end of suffering.


The neither-pleasant-nor-painful feelings also known as neutral feelings, normally make us bored or dissatisfied. Cravings would lead one to seek pleasures (kama tanha) or to become something or achieve something (bhava tanha) rather than sit around all day experiencing neutral feelings that don't bring satisfaction.

No feelings at all, would also be a cause for boredom and dissatisfaction. From the same article by Nyanaponika Thera, we read the commentary of the suttas and his comment:


  Comy.: "From the fourth Jhana onwards, it is the
  neither-painful-nor-pleasant feeling (that is present in these
  meditative states). But this neutral feeling, too, is called
  'pleasure' (sukha), on account of its being peaceful and sublime. What
  arises by way of the five cords of sensual desire and by way of the
  eight meditative attainments is called 'pleasure as being felt'
  (vedayita-sukha). The state of Cessation of Perception and Feeling is
  a 'pleasure, not being felt' (avedayita-sukha). Hence, whether it be
  pleasure felt or not felt, both are assuredly 'pleasure,' in the sense
  of their being painfree states (niddukkhabhava-sankhatena sukhena)."
  
  In AN 9.34, the venerable Sariputta exclaims: "Nibbana is happiness,
  friend; Nibbana is happiness, indeed!" The monk Udayi then asked: "How
  can there be happiness when there is no feeling?" The venerable
  Sariputta replied: "Just this is happiness, friend, that therein there
  is no feeling."


To the arahant, neutral feelings, no feelings and Nibbana are all pleasant.