Couple of questions. Did this occur to some of your images or to all of them? What type of image had lost the flags, imported jpegs from the device camera roll or synced raws from Lr desktop? - Guido
I will describe my whole work flow for easier description.
I took my raw files imported to LR desktop library and made a new collection with all of them (2300 raws). After that I synced that collection with my LR mobile. From my ipad I do flagging on pictures which are just syncing to it. It takes some time to get all 2300 synced. So I work always at first 100, waiting for new to upload and flagging another 100, etc. When I went through first 500 (not exactly 500, but something around), I noticed that first 300 are comletly without any flags. All of already flagged pictures were unflagged, looking as never checked. It already happend to me before. I am not sure, but I think that it is happening if I am syncing collection, which already has some color or even flagging rating made from desktop version before. But I do not know for sure.
So, the answer is: it is happening to my synced raw files from desktop version. And it is happening to some of first flagged pictures. For example - I went through 550 pics which were synced to my Lr mobile. 220 I flagged. But after waiting for uploading more pictures (syncing were still uploading new pics), the count of 220 flagged drop down to 120 flagged. And 100 pics were from a second unrated.
Thanks for the details. We will try to reproduce your issue. - Guido