I just found a use for Stack Exchange Data Explorer, so I created an account yesterday in order to favorite a query. Then I logged in (from a different computer) today, and now I have two accounts.
Both times I used the “Log in using Google” option, since that's what I primarily use for SE as well. I don't see why this resulted in multiple accounts (unless changing my SEDE profile email address did it).
Meta seems to indicate that this situation requires a manual fix, so I am asking for said fix. Or, I could just use the new account, but I have no evidence that I'll not end up with the old account on my other machine. So, also, how do I avoid having this happen in the future, if the merge won't solve the problem by itself?