go to 192.168.100.1 at your computer in a browser. It should pull up a page where you can navigate at the top. If it fails, powercycle the modem and try again. What we are interested in is the signals tab and the logs tabs, can you copy and paste that info in a reply?.
If not read carefully what I type.
Signals: The downstream should be between -8 and +10 with an SNR > 33.
The upstream should be between 35 and 51, you will not see the upstream SNR as you must have access to cmts report for that. It will work to 57 [per docsis 2 standard, 54 for Docsis 3 with multiple channels], but standard fluctuation in cable systems and no access to the cmts receive level [have to be employee] means what I posted is safe, the others are questionable levels. They may work fine, they may be causing your problem when the signal levels fluctuate.
If the levels are in spec we are concerned with Tn errors specifically T3 and T4. T3 indicates an upstream issue usually noise either impulse or consistent, often from simply a losse fittign in the home either on an unused outlet, tv, or the modem itself.. T4 generally indicates a downstream SNR issue but we should see that in the signal levels you provide.
if none of this shows up then the modem may be the issue.