It is sunnah as per all the Fuqaha for those who are performing tawaf to do istilam of Hajr-e-Aswad and kissing it provided one is capable to kiss it and by this act other people are not harmed. But it is not proved from the holy Quran, Hadith, Sahaba, Tabiyeen and Tabe Tabiyeen etc to kiss Hajr-e-Aswad and go in Mataf only for the same act. Also those who enter in mataf only to kiss the Hajr-e-Aswad, they are causing trouble to those who are doing tawaf, hence it should be avoided it.
Allah (Subhana Wa Ta’ala) knows Best
Darul Uloom Deoband