Russia stood with Iran who didn’t want a Christian island within a Shia majority nation. I might be wrong but Putin didn’t warn Azerbaijan because they wanted what Iran wanted.

Is that what Iran wanted, though? And did Iran care? (Nevermind the fact that Russia has long and historic ties and a sort of kinship with Armenians).

To my understanding Iranian-Armenian relations are perfectly fine, and the Iranians never had an issue with that "Christian island within a Shia majority nation-" frankly I don't think anyone did, other than the Azerbaijanis and Turks. FWIW Iran has large Armenian communities as well that live perfectly peacefully- or rather, it has plenty of its own "Christian island(s).."

If anything I'd have expected the Iranians to be more inclined to side with Armenia (usually), if not for the fact that Pashinyan has been dragging the nation (kicking and screaming, resentfully) to the west. The Azeris are major Isntreali allies and more historically western-inclined.

Pashinyan basically gave Nagorno-Karabakh to the Azerbaijanis on a silver platter. I don't think either Russia or Iran had anything to do with it, if anything. And if they had- I'd have expected them (both) to side with Armenia, if not for the fact the current regime is a total western stooge. To the Iranians, Azerbaijan may be Shia- but they also assist in Israel/NATO flanking their country, have nationalistic claims on large parts of Iran, and have considerable poisonous "pan-Turkic/Turanist" sentiments which only serve to destabilize, flank, and carve up Iran even more.