WiFi is very slow on 2.4Ghz

[Wariat]

Speed test on my Wifi show between 2 and 8 Mbps on our phones/tablets, on my laptop I can't even get it to conduct a test, the interent is barely usable. Power cycling has not helped. My Xfinity account is for 250Mbps. The latoptop gets that on the ethernet. The phones get about 150Mbps on 5Ghz, which I assume is normal. I noticed it slow down on our phones around the time we installed a Ring doorbell. It may just be a coincidence, but it go me digging more. I set up another router as an access point, which the doorbell is now on, but the modem WiFi is still slow. The speeds on the access point router are good. I'm not sure where to go next with it. My channels are different too... the C7100V is on channel 1, and the access point router on channel 6. But again, this became an issue before I set up the access point.

[FURRYe38]

Has a factory reset and setup from scratch been performed on the modem? 

Use a wired Pc and speed test with Ooklas installable speedtest app. 

Be sure no coax cable line splitters are in between the ISP service box and modem. 

[Wariat]

With a wired connection, using the Ookla software, the latest test reached 275Mbps, which is great. I have not tried a factory reset... I suppose that a factory reset is the next step...

[Wariat]

I performed a factory reset on the modem. I made no changes. I still have trouble passing 10Mbps on the download standing 3 ft from the modem. When on 5G WiFi, that can reach 250Mbps

[FURRYe38]

What device do you have connected on the 2.4Ghz frequency when speed testing? 

Do all wireless devices exhibit this condition when on 2.4ghz? 

What channels are you using? Auto? Try setting manual channel 1, 6 or 11 on 2.4Ghz and any unused channel on 5Ghz.
Any Wifi Neighbors near by? If so, how many?

Try looking for 20/40Mhz coexistence Under Advanced Tab/Advanced Settings/Wireless Settings and if you happend to see this, uncheck the check box. This will set 40Mhz only channel width. 

[Wariat]

I've been primarily speed testing on my phone (android). I've checked on my wife's phone a couple times as well. I think the laptop can only use that band, and the laptop is the worst. Usually that times out and doesn't do the test, and when I did get it to go last try, it was barely 2 Mbps. My kids's TVs were on it before (had connection issues, which is another reason I created an access point to put them on). Seems like everything that goes on it is slow.

Prior to factory reset, it was on channel 1 (access point router was on 6). After the reset, it was in Auto when I retried the speed test, and then I set it to 1 again. Both of those times I had unplugged the other router, and the speed tests did not improve on either channel setting.

I have one neighbor that's a stone's throw away and another that's probably 100yds away. I can see a couple other WiFis, but the signals are very weak.

I will check the 20/40 coexistence tomorrow, at work now, and see if that helps. Thank you for all your feedback by the way. I still haven't gotten Xfinity to call me back as they promised. Starting to wonder if all else fails, to set up another router as an access point and give up on putting any devices on this one anymore.

[FURRYe38]

Try the modem on channel 11 and the AP on channel 1 as a test. 

You can disable the wifi on the modem and put on a different AP as the main wifi source. 

[Wariat]

Sorry for the delay. So I did not see 20/40Mhz coexistence in the section mentioned (or anywhere else). I did try changing the channels as recommended as a test, but it unfortunately did not make a difference. My only other guess is something on Xfinity's end. I had gone online requesting customer support to call me, they said there was a zero minute wait time, hoped to get a call within a couple minutes, but instead they never called at all  I might try again my next day off, but for now planning on setting up an access point to replace it. Thanks again for your input!