Tajikistan had good reason to not liking Iran. I haven't kept track of recent news, but seeing that Iran has made progress on SCO, I assume these issues have been resolvedI don't think one can make the connection between signing many deals and Tajikistan "blocking Iran". The two aren't even bordering one aother to be at odd.
The two are both Iranian speaking countries, which makes the deals look more like deepening already good relationship than mending conflicts.
6 year old article
Tajikistan Opposed to Iran’s Full SCO Membership
While Russia has repeatedly backed Iran’s full membership in the Shanghai Cooperation Organisation (SCO), some other members, particularly Tajikistan, seem to be opposed to the accession.
According to a report by , Tajikistan is said to be one of the main opponents of Iran’s accession. The two countries have many commonalities, including their ancient Persian culture and language, and used to have the closest and most stable relations.
Iran interfering in Tajikistan politicsHowever, these warm relations took a nosedive in late December 2015 on the issue of the Islamic Movement of Tajikistan. While the Islamic Revival Party (IRP) was considered by the Tajik government as a banned party, its leader Muhiddin Kabiri was invited to an international conference in Tehran, and this outraged the Central Asian state.