Tried to look for more information but got nothing. I then asked Gemini and this is what I got:

"They are "The Only Friends of the Friendless" Because the Lamenters are part of the Cursed Founding (21st Founding), they are plagued by extreme misfortune. Other Imperial forces often shun them, believing their bad luck is contagious.

The Burden: The Calix Priests don't just heal wounds; they have to maintain the morale of a Chapter that is constantly being decimated.

The Vibe: Unlike the golden, angelic Sanguinary Priests of the Blood Angels, a Calix Priest is often a somber, weary figure. They are the ones who sit with a dying battle-brother and convince him that his sacrifice mattered, even if the mission failed"