Lack of motivation in ADHD can be the result of  ‘Conflicting conscious and subconscious emotions’.

We are still learning about how Emotions work.
It is the most studied field in neuroscience to date, the updated version of Anxiety as in the pave-way of all mental disorders.

Latest findings in ADHD suggest Subconscious Emotions-dormant feelings-are picked up first by the Autonomous Nervous System.

Subconscious emotions are most often rewardless.
The ADHD brain is constantly craving for reward.

We have no control over subconscious thoughts, therefore a real emotional conflict will arise, resulting in hyperactivity and loss of focus.

Flashbacks are the popular definition of subconscious emotions. They are always traumatic, since the brain is programmed to process Present Information.
Everybody has subconscious memories at a dormant level, but the ADHD brain never sleeps. 

Apparently, dopaminergic medication can’t distinguish between emotions.
Subconscious thoughts are normally not recalled at conscious level, though detected by the Autonomous Nervous System, particularly in stressful situations.
An example is waking up in a bad mood without apparent reason.

The neurotypical brain selects emotions. In ADHD, the process is aggravated by Emotional Conflict. 

Speculation is that the Amygdala, the gland at the center of the Limbic System acting as emotional modulator, goes into overdrive in ADHD.
There is no cure yet, other than dopaminergic medication enhancing reward.
Stimulants help to a good deal however, they cannot reverse unpleasant emotions. 

The more effective action to date is Prioritizing, working on rewarding tasks first and using the extra dopamine later for bothersome tasks.

The goal is achieving Emotional Regulation.
Emotional Conflict is a subcategory of Emotional Dysregulation, specifically the inability to control emotional outbursts.
You may recall the Magnification of Stress in ADHD as the result of Prefrontal Cortex Impulsivity associated to an overactive Amygdala, accounting for the real Conflict.
Again, the sufferer indulges in dangerous behaviors without thinking of consequences, all in a desperate attempt for Reward.
Administering an extra dose of Stimulants is the action of choice.
ADHDers are usually reassured by the release of craved dopamine, approximately within 30 minutes, during which they might go into Shutdown, not a medical emergency.

Nonetheless, Stimulants target Reward Networks.