Failing to set _owner on insert (sporadic?)

Hi all,
I am managing to insert profile information into a collection at user signup, but for some reason setting the _owner value has only worked for me once (and I don’t remember changing this code). Is there anything more I’d need to do to allow setting the _owner field?

 
return wixUsers.register(email, password, {
 "contactInfo": {
 "emails": emails,
 "labels": labels
            }
        })
        .then((results) => {
 let userNameLowCase = userName.toLowerCase();
 let userProfileToInsert = {
 "userName": userName,
 "userNameLowerCase": userNameLowCase,
 "_owner": results.user.id,
            };
            console.log(userProfileToInsert);
            wixData.insert("userProfile", userProfileToInsert)
                .then((insertResult) => {                                  
                    console.log(insertResult);
                })
                

The rows are being inserted into the collection, but the _owner field isn’t getting saved. I did manage to do so once, so it’s probably not related to permissions. userProfile includes _owner, but insertResult does not…
Appreciate your input on this!

All the fields starting with an underscore like _id, _createdTime etc… are set automatically by the system. I don’t think you can write to them (but I might be wrong).

Thank you J.D.
I found this https://www.wix.com/corvid/forum/community-discussion/changing-the-owner which indeed says that but has a workaround by @dan which seems to work: adding a beforeInsert Hook.
The weird thing is, I was somehow able to enter one record with an owner id before doing the hook. Maybe that was the bug… I’m worried by the apparent inconsistencies which keep on coming up in Wix…

You can set the _owner field with

https://www.wix.com/corvid/forum/main/comment/5d4aaf8421f60b0017324951

Probably works as well for the other field