I have been encountering an interesting problem for 2 months.
I have an object type which keeps a nested object inside. There are also several DBRefs in the main object. For the unknown circumstances (I do not exactly know how the problem is triggered), nested object begins to be not written under the main object for that collection during save operation. But DBRefs are fine.
So when I drop all the indexes for that collection and recreate them programmatically, this nested object problem is solved and begins to be written accordingly; until another time.
Do you have a suggestion/opinion about this?