Knowing we're QC'ing all units 5 times on the assembly line, it's most likely fine. :-)

It's most likely a simple misconfiguration. By default Output 2&4 are configured with crossovers for a 2way speaker DSP configuration. You'll need to bypass the filters if you're not using it as such
Go to the output section, Crossover (Xover) and click on Bypass if you want full range. You can check out the manual to learn a bit more on how the crossover section works.