Unless my install is broken ; there is a bug when changing the owner of XFMG albums : the tool ptus the userid (numbers) intot he username field.
Indeed for whatever reason, XFMG mysql tabels store the userid AND the username (which is stupid).
Fyi
This has been a confirmed problem for a while https://xenforo.com/community/threads/interaction-to-next-paint-inp.215845/
I'm still trying to pinpoint what google thinks is a problem...