Download speeds significantly lower than usual, but upload is normal for my C6250

[MichaelGBaker]

So basically my router/modem has horribly slow download speeds. I pay for, and for months have received 150 Mbps download and 10 Mbps upload. As of a few days ago, my download speed has dropped to 1-10 Mbps but my upload speed has stayed consistent at 10 Mbps like before. I've factory reset the unit, tried new coaxial cables, turned it on and off, unplugged and replugged the power, and pinged the unit via the diagnostics. What is going on here?

[FURRYe38]

Have the ISP check the signal and line quality UP to the modem. 
Be sure there are no coax cable line splitters in the between the modem and ISP service box. 

Check the speeds with a wired PC, not wireless...

[MichaelGBaker]

I already checked/did all those things but the problem persists.

[FURRYe38]

Try a different PC? 

Ask the ISP to reprovision the configuration file to the modem. Power OFF for 1 minute then back on and re-test with a wried PC. Turn OFF ALL other wireless and wired devices. Speed test with Ooklas installable speed test app. 

If the problem still continues, you have have a faulty or modem going bad. 

[MichaelGBaker]

So I've found that keeping the power disconnected for over 1 minute restores my internet to its functional state, but only for about a half hour to an hour because it went back to its problematic state.

[MichaelGBaker]

Spoke too soon. It returned to its problematic state in just a few minutes this time. Issue is still ongoing.

[MichaelGBaker]

I can confirm this issue only seems to happen from the mornings to the afternoon. At night, every day, my internet has been restored to 150 Mbps. But in the morning, it experiences the same issues. I have no clue why

[MichaelGBaker]

Issue is ongoing. I've discovered that turning off my router for 3-5 minutes temporarily solves my issues, however, it always reverts back in less than 24 hours. Other people on my ISP are experiencing similar problems. Is it possible a firmware update messed with our machines?