After beating Caiatl, my duo and I got caught in an endless loop of near escaping the nightmare realm. Kys half fixed the issue where we ended up in Caiatl's room. But never returned to Erris and the loot chest. We do not know if we could have even earned Heartshadow. It was our first clear of the week and we did nothing out of the ordinary. Super anticlimactic and hopefully fixed soon.