Stop in for a cup of coffee
I had a Comcast modem do that a while back.
I switched from AT&T. They really sucked. I found out when I dropped them that they have a software problem in their modems for the last year and a half and weren't trying hard to fix it...
They couldn't support me at 6 mbps.
I get 15 mbps from Wow cable and they have hit 15.5 on speed tests. I never reached what AT&T promised me. I was originally at 12 with them, but they couldn't maintain it as "I was at the end of the line (last connection) and was sucking hind tit... So they lowered me to 6 mbps and still couldn't keep it going, sometimes my speed was below 1 mbps...
I had over 20 service rep appointments in about 6 months including having my line replaced to 3 poles, new modems, and they still couldn't get me a consistent signal. One rep took 6 1/2 hours to show up and then another hour and a half to do the work. I wasted 8 hours waiting for their guy to show up. I started telling them that I'm spending as much time (or more) than they are to keep my signal going and I want full time pay with benefits...