Strange spikes/dips when stacking

I am getting some strange graphing behavior when trying to stack two things together. When these items are graphed individually or unstacked, the graphs look normal. When they’re stacked together, there are these strange dips in one of the item’s graphs. Hovering over the graphs and seeing the tooltips doesn’t show any reason why these dips would be occurring. Any thoughts why this is happening?

Specifically, these are graphs of the inbound octets on two different interfaces gathered via SNMP. I don’t see anything in the data that would explain these dips.

I’m using Grafana * Grafana v8.3.6 (bf8766b) on Windows 10.

I’m trying to stack the inbound octets of two interfaces so I can see the cumulative inbound traffic.

I tried with both the “Time Series” and “Graph (old)” visualizations. I simply added each interface’s inbound octets data, set them both to: mean(); derivative(1s); math(*8), then tried both the “Stack” function in the “Display” panel, as well as the various “Stack” options in the Series Overrides" panel (in the “Graph (old)” visualization).

I expected the two otherwise normal looking graphs to stack without these anomalous dips. I did not receive any errors.

Here are the configs with the unstacked graphs:

Here are the graphs with the same configs with Stacking turned on: