It makes a lot of sense to me your explanation, it is what I was thinking.
I went to the Register of Deeds today and there was a third child who died, there was an Anna Fix born 3 Jan 1885 and died 18 Dec 1888 with the same parents, I unfortunately did not write down what she died from. I spoke with the woman in charge of the office about the fact that we could not find any other birth record than the one for Olaf (or August) in 1887 and she mentioned that if the birth was not attended by a physician, nurse or midwife, it was possible that it was not recorded, very sloppy records during that time. Shell Lake at this time was a big logging town, lots of people coming and going(I think the population was over 2000); we also talked about the fact that the parents Anna and Anders Fix could have been working in the logging camps and died in another county, if the grandparents were here in the area. Have you checked any of the other counties around Washburn?
I went to the library and looked at the Shell Lake Cemetery records and found where the family is buried, I went to the cemetery but I need to record other families who are buried around them to see if there are any headstones. The cemetery records do not have any dates, I am not sure if I will get to the library tomorrow or it will be Monday. If you send me your email address I will send you any photos that I might find.
I was looking at August Fix's records and I see that on his WWI draft record it lists his grandmother as his dependent. Have you found her death record? Have you done any research with the Swedish records?
My email address is firstname.lastname@example.org