Shaykh Al-Islam Ibn Taymiyah said in his Majmoo v 28 p 212:

"So when there is not in his boycott deterring for anyone or ceasing for anyone, rather it leads to cancelling many of the good things prescribed, then boycotting him is not ordered, as mentioned by Ahmad to the people of Khurasan when they could not stand against the Jahmiyah, so when they are not able to manifest animosity to them, so the order to do this good action (showing animosity) is cancelled, their objectives in it is to protect the weak believer, and maybe there is in it taleef (attracting/call) to the strong Fasiq. Likewise when Qadr became widespread in the people of Basrah, if their narrations were abandoned, it would lead to extinction of knowledge, Sunnan and Athar preserved in them."

Shaikh Al-Islam Ibn Taymiyah also said (28/206):

“And this boycott is differs according to boycotters depending on their strength and weakness, their little or great number, if the intent is to punish the boycotted person and correct him and the return of the laymen from a condition similar to his, so of the Maslahah is preponderant in it in such a manner that his boycott will lead to weaken his evil and hide it, then it is legislated. But if neither the boycotted person nor anyone else cease it rather it increases in evil, and the one boycotting is weak, so the harm in this will be greater than the benefit, then boycotting is not legislated”

Shaikh Bakr Abu Zaid said in his book “Hajr Al-Mubtadi’” p 49-50:

“The principle in the religion is boycott of the innovator but it is not general in all conditions and for everyone and with every innovator…and the legislation of boycott is encircled on religious principles based on bringing benefits and removing harms, and this differs with the difference in innovation itself, and with the difference of innovators, and with the difference in the condition of those who boycott, and the difference in the place, strength and weakness, the little or great number…”

Sh Bakr Abu Zaid said in his book “Hajr Al-Mubtadi’ p 50-51:

“Shaykh Al-Islam (Ibn Taymiyah) said about the correct methodology regarding boycott: “Some people established this (Boycott) as general, and they used boycott and opposition as they were not ordered, (boycott) that was neither obligatory nor recommended, and sometimes they abandoned through it obligations and recommendations, and did through it forbidden matters. And others turned away from it (Boycott) absolutely and they did not boycott the one ordered to be boycotted among evil innovations” (Fatawa 28/213)

Shaykh Ibn Baz said (as quoted on Islam-qa)

“The most correct approach is to look at the shar’i interests involved, because the Prophet (peace and blessings of Allaah be upon him) shunned some people and not others, depending on the objectives of Islam. He shunned Ka’b ibn Maalik and his two companions (may Allaah be pleased with them) when they stayed behind from the campaign of Tabook with no excuse. He shunned them for fifty days, until they repented and Allaah accepted their repentance. But he did not shun ‘Abd-Allaah ibn Ubayy ibn Salool and a group of those who were accused of hypocrisy, for shar’i reasons. 

The believer looks at what is in the best interests (of Islam). This does not contradict the idea of hating the kaafirs, innovators and sinners for the sake of Allaah and loving the Muslims for the sake of Allaah. Attention must be paid to what is in the general interest; if shunning is better then they should be shunned, but if the objectives of Islam dictate that ongoing da’wah efforts should be made rather than shunning, then that is what should be done, following the teaching of the Prophet (peace and blessings of Allaah be upon him). And Allaah is the Source of strength. Majmoo’ Fataawa wa Maqaalaat Mutanawwi’ah li Samaahat al-Shaykh Ibn Baaz (may Allaah have mercy on him), 9/423.

Shaikh Albani said: “In summary, the principle of cutting off/ostracizing today is out of the question because we are in a time when the Muslims are weak.”

Source: https://shaikhalbaani.wordpress.com/category/methodology-2/boycotting-another-muslim/

Shaikh Ibn Utheymeen said in “Sharh Huliyah” p102:

“When wee see the Maslahah (benefit) in this, then abandoning boycott is better, and when we see a benefit in boycotting by the fact that Ahl e Sunnah are strong and these (innovators) are weak and defeated, then boycotting is better”

Shaykh Muqbil said:

“The reality is that there is a Khariji notion which entered in nowadays people, the notion of Jama’ah At-Takfeer, they enlarged the topic of boycotting the innovator, and when we read the biography of the Messenger of Allah (saw), we see that boycott is narrow, he (saw) boycotted the 3 who remained behind the expedition of Tabook, and he boycotted his wives for a month so to educate them, and he boycotted a very small group. So it is necessary to look at the benefit in boycotting, so when boycotting has an effect and the person will return to the truth, there is no problem in boycotting him. But when it increases him in insolence and aversion, then no…”  

http://muqbel.net/fatwa.php?fatwa_id=3912