Assalaamu alaykum. In Musnad Ahmad ibn Hanbal, there is a hadeeth that Imam Ahmad wanted his son Abdullah to remove from his Musnad because, in his view, it was contradictory to other ahaadeeth. The hadeeth is number 7663: Narrated Muhammad ibn Ja'afar from Shu'bah from Ibu At-Tayyaah from Abu Zur'ah that Abu Hurayrah said: "Allah's Messenger, sallallahu 'alayhi wa sallam, said, "This branch from Quraysh will ruin the people." The Companions of the Prophet, sallallahu 'alayhi wa sallam, asked, "What do you order us to do (then)?" He said, "I would suggest that the people keep away from them.'' Abdullah ibn Ahmad (i.e. son of Imaam Ahmad) said, My father said in his fatal disease, "Remove this hadeeth because it is contradictory to the other Ahaadeeth narrated from the Prophet, sallallahu 'alayhi wa sallam, i.e. the Ahaadeeth that read, "Listen and obey (your rulers) and be patient with them".
The chain of narration is authentic according to Shu’ayb al-Arna'oot and other scholars. And strangely enough, his son left it in the Musnad with the backstory! Anyway, how could he have asked for such a request from his son? Is this not what the scholars of the Jews and the Shiites do with hiding Allaah's truths? How can the so called imam of the prophetic Sunnah do something regarding which Allaah has cursed the one who does it for all eternity?

All perfect praise be to Allah, The Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad is His slave and Messenger. 

It is Islamically required of a Muslim to think well of his Muslim brother, as Allah says (what means): {O you who have believed, avoid much [negative] assumption. Indeed, some assumption is sin...} [Quran 49:12]

Ibn Katheer said in his Tafseer (exegesis):

“Allah, the Exalted, forbids His faithful servants to have negative assumptions, which means having doubts and suspicions about one's family, relatives, and other people in general without a valid reason, since some of such assumption is pure sin. Therefore, the Muslim must avoid much suspicion to be on the safe side. `Umar bin Al-Khattaab, may Allah be pleased with him, said, 'Never think ill of the word that comes out of your believing brother's mouth while you can find a good interpretation for it.'”

This is even more emphasized concerning the scholars and virtuous people, especially regarding someone with the status of Imaam Ahmad.

Thinking well of a Muslim requires finding excuses for him, and that is what the scholars did in regard to this statement of Imaam Ahmad. Shu’ayb al-Arna'oot quoted Shaykh Ahmad Muhammad Shaakir, as saying, “Perhaps it was caution on his side lest people would think that deserting them (the rulers from among this branch from Quraysh) means rebelling against them; which would lead to great evils like breaking up (the rows of Muslims), disunity, and disobedience to the ruler. However, in fact, what is meant by deserting them is that a person should take precautions for his religion and not engage with them in corruptive pursuits.” 

According to Imaam Ahmad, this hadeeth is Shaath (i.e. a hadeeth in which the trustworthy narrator contradicts other narrators who are more trustworthy than him – and it is one of the categories of the weak hadeeth).

Imaam Ahmad neglected some other ahaadeeth than this hadeeth because of considering some of their narrators weak, among which is the hadeeth that reads, “The household of Muhammad never ate to their fill of wheat-bread with meat until he died...” Abu Abdur-Rahmaan (Abdullah, the son of Imaam Ahmad) said, “My father neglected this hadeeth because he was not pleased with (the trustworthiness of) the man from whom Yazeed narrated." Imaam Ahmad also neglected the hadeeth which reads, “Whoever dies of my nation while drinking alcohol, Allah will forbid it for him in Paradise.” Abdullah said, “My father neglected this hadeeth, and I thought that he neglected it because it is incorrect, but it was because the narration is from Maymoon ibn Ustaath from Abdullah ibn 'Amr, and it does not mention that it is from As-Sadafi.”

In brief, Imaam Ahmad had his own considerable view when he ordered to neglect a specific hadeeth.

You should also know that the scholars established that it is permissible to conceal some knowledge for an Islamic benefit and not because of desires only, based on the hadeeth of Mu’aath, which reads, “...Shall I not give glad tidings to the people (i.e. tell the people that the right of the slave of Allah over Allah, Glorious and Sublime, is that He does not punish him who associates not anything with Him)? The Prophet said, 'Do not tell them, otherwise they would rely on it alone.'” [Al-Bukhari and Muslim]

Also, it is confirmed in Saheeh Muslim that Ibn Mas’ood, may Allah be pleased with him, said, “It is the case that you do not relate a narration, to the people, which their minds cannot grasp except that it becomes a Fitnah (tribulation) for some of them.” [Muslim]

Al-Bukhari narrated from ‘Ali, may Allah be pleased with him, that he said, “Talk to the people according to what they know (i.e. to what their minds can grasp); do you want that Allah and His Messenger would be belied?”

So not everything that is known is said; rather, the situation and the circumstances should be taken into account as a way of fulfilling legitimate purposes.

As for the people of whom you mentioned that they hide the truth, they do so out of following their own desires, rejecting the truth, and repelling people from it, and it is not because of taking legitimate Islamic purposes into consideration.

Allah knows best.