First of all, nobody knows everything, and all these are just some ideas, maybe right and true, maybe mistake, God knows…

Probably the main issue here is transportation roots.

The 2020 war between Azerbaijan and Armenia had significant consequences for Tehran.

Till autumn of 2020, those territories were controlled by Armenia; therefore Iranians had no issue passing through the territories.

The situation actually looks like started to change in September of 2020.

When Armenia controlled the 7 surrounding districts of Nagorno-Karabakh/Artsakh, Iran primarily utilized the Goris-Kapan highway for transporting goods and etc. However, 21km of this highway is now in territory that Armenia surrendered.

Azerbaijan, blocked part of the road that goes through Azerbaijan for Iranian trucks,

Right now the corridor is in Azerbaijan hands and Iran doesn't have access to it anymore.

In addition, with the cooperation of Turkey, it looks like that, maybe, they intended to occupy more parts of the territory of Armenia bordering Iran and cut off Iran's with Armenia.

Armenia is a strategic ally of Iran and vice versa.

The road which links Iran and Armenia is extremely important for Iran, since through that route Iran also access Georgia and through Georgia it accesses Black Sea.

Iran also relies on Armenia for key land routes with Georgia and Russia.

The actions of Azerbaijan were not welcomed in Iran and caused the current crisis.

Although the people of Azerbaijan are a Muslim nation, the government of Azerbaijan is a secular government. This maybe has caused the Azerbaijani government to feel threatened by the Islamic Republic of Iran. The government of Azerbaijan fears that its people will be interested in the Islamic Republic and want a similar government in Azerbaijan. Azerbaijan also tends to call Iranian Azerbaijan “South Azerbaijan” to piss Iranians off. However, Iran has repeatedly stated that it respects the opinion of the Azerbaijani people. The Azerbaijani government also has promised to not to jeopardize the friendly relations between the two nations of Iran and Azerbaijan.