Season 2 WT End Game Boss No showing up

Hello, my friend and I play Diablo4 together. We’ve been loving the second season until we reached end game. The end game bosses require material sacrifices that are grinded for, we coordinate for each event from world bosses to helltides. WE have not been trading each other (as 1 trading is banned and 2 that’s way too much effort when we both play together so we collect the same amount of mats basically). However we has not been enjoyable is spending mats for the boss to bug out…we’ve recently run into this with Lord Zir hard mode (which requires world boss mats). Would would spend the mats and after dying, Lord Zir will disappear and not return…
It feels like our gathered mats were spend for no reason. why grind for this again? This is the second time its happened to us