Thanks for the reply, @Nerdburg! My question is really why would the Arris show errors and the Motorola show none with the exact same connection?
With signal levels being that good, why would my testing show speed fluctuations? The only device directly connected to the modem is the Eero, which has it's own speed test functionality. 368-874 is my range in recent testing.
I have an ARRIS SB8200 and used it for nearly a year. I've found this modem to be very sensitive in general, probably because it tends to run hot, and I would see a lot of corrected errors on it as well. However, the DOCSIS 3.1 standard has Forward Error Correction built into its technology, so all those corrected errors are actually normal and aren't going to be a problem. It's the Uncorrected Errors that indicate issues with your connection.
As far as the fluctuations in speed, bear in mind that there might be other devices connecting to your remote server at the same time, and more congestion will impact the results of the speed test.
I can't speak for eero, though, so you'd have to ask them about the technical aspects of the router's internal testing.
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