Despite being engaged in Krsna consciousness, for many years, how come that a devotee can still be exhibiting the symptoms of a conditioned soul?

"Many years" may in our case not mean "many years" for the Supreme Lord. After all, His "instant" mercy may prove to be very different from our concept of "instant". When Lord Vishnu falls into His slumber, we had been undergoing many many millions of life times. His one minute is for us like eternity.

And so having different perception of time, we may get occasionally impatient.

There is one letter written by Srila Prabhupada which reveals the "secret" why despite even prolonged exposure to Krsna consciousness a devotee may manifest still severe anarthas. Its written to one of Srila Prabhupada’s leading preachers, somebody who himself had to experience after Srila Prabhupada’s departure how his conditioning caught up with him and so he had to return to a karma-contaminated field due to his unpurified material desires. Nevertheless his exceptional service to Srila Prabhupada makes him to operate with a spiritual credit which without a doubt will allow him when his materially conditioned existence is over to reactive his entire spiritual potential.

On 6th of November 1969 Srila Prabhupada wrote to him:

“Regarding your final question, it is a fact that when one is in contact with Krishna, His Name, His Qualities, His Form, His Pastimes, immediately he becomes purified. But because we are conscious living entities, the proportion depends on our conscious acceptance. It is stated in the Bhagavad Gita that Lord Krishna responds proportionally to the service of the devotee. Another example is that the sunlight is open for everyone and for every place, but to enjoy the sunlight or to take advantage of the sunlight depends on the proportionate arrangement by the receiver. Prosecution of devotional service means gradual purification and proportionate revelation of Krishna Consciousness…”

(I am sure that Srila Prabhupada is using the word "prosecution" in a sense of "proceeding" in Krsna consciousness and not "prosecuting" it:-)

And so we can understand that the path back home back to Godhead is not automatic , but it requires full participation of the one who walks on it. After all, Krsna is revealing Himself proportionally to the surrender of His devotee.

Therefore designations only, the day of ones entrance into Krsna consciousness, ones bodily "seniority", the academic education one received, any material designated identity, plays no role in the way a devotee truly progresses in his approach towards the Supreme Lord. As kanistha adhikari insist to be recognized as uttama adhikari, madhyama and uttama adhikaris abstain from such false designations and strive for more cultivation of one’s "conscious acceptance" of Krsna consciousness instead of licking on its surface only in vain attempt to taste the closed jar of nectar.