This is why having data with real fuel is valuable.
Viscosity loss comes from both fuel and shear. So, you have two things driving down viscosity. You don't have control over how much shear takes place, it's pretty much a constant, but fuel dilution varies depending on how the vehicle is driven and this is something that can readily be tracked with GC. So, if fuel goes up but viscosity doesn't go down, then something is pushing it the other way, and that would be oxidation.
As I said in our previous exchange, while I don't condone what you are doing, I follow it with interest, so I'm glad you continue to provide these reports.
Oxidative thickening isn't unusual, but it would be surprising to see it at such low mileage. Some formulators (perhaps most) when dealing with inexpensive commercial (typical) VII polymers will try and balance shear with oxidative thickening so that the viscosity is relatively stable. @High Performance Lubricants
has talked about how that doesn't happen with their oils because they use very expensive VII's that don't shear, so oxidation tends to drive up viscosity with long OCI's, but that's not what happens with your typical commercial oils. The wildcard then in this scenario is fuel, which will still drive viscosity down overall.
So, in the case of your two reports we have two similar mileage OCI's in the same engine. We assume shear is going to be roughly the same between the two; identical for the sake of this comparison, because the mechanicals are a constant. Both have fuel in them. However, the most recent has both more fuel and higher viscosity than the previous run. What would be the driver behind this? Oxidation, which also may be a result of the fuel dilution that, when combined with heat, degrades the oil more quickly.
Any idea on the ETA of your report from OAI?