Why was the aforementioned transaction considered usurious (mudharabah) in Fatwa No. 58084, even though the contract mentioned only profit and not loss? And does the omission of mentioning loss invalidate the contract?

The wording mentioned in question number 58084 is a Mudarabah contract, because in Mudarabah, what indicates it suffices, without the need to mention details of who bears the loss. Al-Kasani Al-Hanafi said that the pillar of the contract is offer and acceptance with words like "Mudarabah" or "Muqaradah" or "Mu'amalah," without mentioning details of the loss. It is stated in Asna al-Matalib that it suffices to say "I enter into a Qirad with you" or "I enter into a Mudarabah with you" or "I enter into a Mu'amalah with you."