What are normal signal levels?

Service interuptions multiple times a day.  SB8200 Modem. Only one 2-way splitter installed by the tech. 

Outage coincides with error log "Started Unicast Maintenance Ranging" followed by multiple "Commanded Power in Excess of 6 dB Below the Value Corresponding to the Top of the DRW" and "Dynamic Range Window violations"

After weeks of chats with tech support and the automated phone support that just wants to reboot my modem I finally got a live person who tells me you signal is within normal limits but can't tell me what those limits are.  Obviously my modem doesn't agree.

I believe these downsteam numbers are on the ragged edge of being too low. The modem panics and rescans, causing the outage.   I can't get any human tech support that knows enough to help me troubleshoot this.  All the other posts I"ve found show signal levels in the positive range for DS and I'm -10 dBm or worse.  If the system is asking for more upstream than the modem is willing to give, wouldn't that indicate a problem?