No, sorry.
I use wixMembers_onMemberCreated(event) at the event of the member being created but then I use contacts.updateContact to add the custom fields I need. Like I wrote, I can get it to work this way so I haven’t really searched very hard for a solution to use updateMember but I’m guessing it has something to do with collection permission. Since the member isn’t actually logged in when the event is triggered due to email confirmation and the member collection needs an approved role to be edited I think that’s where the problem lies. But like I said, in my case I can go around this. What are you trying to do?