This has happened to me as well. Thankfully I haven't played Arcade much yet and only got up to Level 10. I am currently Level 2.
I think an issue may be that I play the game on two separate Xbox One machines. I play at home on my Xbox One X, and a few times a month I travel to a friend's place and play on my Day One Xbox One console that I bring with me. Perhaps something is happening during the file sync between machines?
I tested on both machines last night and my rank did not reset. It was at 8 when I synced to my Xbox One and played one round, and leveled up to rank 9 on my Xbox One X when I synced and played one round. I don't know if this was ever thought to be a cause but I wanted to test it anyway.
I'll post again if something happens in the future but it appears the issue is resolved for now, at least for me.