Downstream light keeps blinking

If the downstream light is blinking, it means only 1 channel is locked and its searching for more channels. 

You need to post a screen snip of the cable connections page and the event logs for us to help you better. 

But you can start with a few troubleshooting tips. 

Start with removing any amplifiers, signal attenuators, or splitters from the coax.
From there check the line for kinks, damage, moisture in the line.
Check the connectors for improperly made ends, foil touching the copper coax line, bad/old/cheap connectors, or corroded connections. Replace them if you do.
If you can, simply connect the modem right where the coax comes into the home. This prevents wiring in the home from being the issue. And some ISP’s charge if the wiring issue is in the home. So this helps prevent this.