Helltide question (bug or intended)

I don't know much about Helltides besides things I've experienced. I've done a couple so far and to me it was like you kill stuff/do events for cinders, and then use those to unlock chests which each give you one guaranteed legendary. Or 3 if it's a mystery one.

Just did one, where a) two chests disappeared after I went back to open them around 20 minutes later, and b) none of three chests I did eventually open (two for 125, one for 75) had a legendary in them. The last one for 125 had one single sacred item and a health potion. No packages delivered to my stash so far either.

Since that seemed weird to me:

Did I just get really lucky the first couple of tides or was this one bugged?