Unfortunately, I don't know if this occurred before or after the latest update, since it updated automatically on my iPad.
I moved an account from one group to another (specifically, from a group named "Hidden Accounts" to one named "Credit Cards").
When I next used the app, I noticed that my "Hidden Accounts" group no longer existed. All the accounts that previously belonged to that group now belonged to no group.
I've manually recreated the missing group and readded all the accounts - but now I'm wary of moving accounts again, in case I have to redo all that work!
I'm really sorry about that! I do not recall any other user reporting this issue, we might need to investigate. If you'd like us to look into it more closely, please contact us via e-mail - definitely if it happened more than once!