The parent comment posted in that thread, so I assume he has read it. While I read parts of the comment thread earlier when if first came up, I searched some key phrases and couldn't really find specifics other than the SO link you already mentioned. There was a lot of discontent and general ramblings about Google support being terrible, but I saw more people praising the paid support options and support in general for paid products than giving concrete examples of being burned.
I don't know if you have read the original thread, but there are a few examples of this: https://news.ycombinator.com/item?id=14356409
Also this: https://stackoverflow.com/questions/38959321/firebase-databa...