Document unexpectedly changed while view indexing

At first, I should thank for your great product.
I’m loving it.

BTW, I encounterd weird situations.
I have 3.0.2 clusters with 2 nodes and I added up 2 more views on that.
And then I published 2 new views and it followed by whole new long~ long~ indexing process.

After all this process, one of my documents has been changed unexpectedly.
More specifically, one of the fields that lengths about 200bytes has been missing completely.

I don’ have any idea.
please tell me what I have to do to keep away from this situations.