There are several issues, and I think they all have to be connected somehow, so bear with me while I try to explain.
1. Using iMessage, backing up to iCloud, etc. on Apple devices - ours and people that just come over and use our network: iMessages will not send pictures. The bar goes to about 95% then the send fails and it sends as a text message over cellular data. This is not an issue for our devices when going to other home networks, and becomes an issue for others only when using our network. It works fine if we connect to the free xfiniti hotspot, or cellular data. Similarly, iCloud backups never happen when plugged in and connected to wife here, but happen automatically like they should when we go to another network.
2. Using VPN: I have to use a VPN to work from home, which I do about 50% of the time. If I connect to the xfiniti hotspot, no issues. If I connect to our network, it constantly drops the VPN, won't send email traffic, and all sorts of other issues.
3. So slow. We have 150 mbps service (or should) and are lucky to get above 10 mpbs on a speedtest. That's just one device on the network. Heaven forbid someone want to watch netflix and check twitter.
4. Connection constantly drops - modem needs to be restarted (both the Comcast one when we had it, and now our own) a couple of times a week.
Things we've tried:
Replaced all of hte coax, the splitters, the ethernet cables.
Replaced the xfiniti gateway modem with our own modem and router
Power cycled everything hundreds of times
Reset network settings on all of the apple devices.
Tried using Google DNS
Selecting the least busy channel rather than using auto-select
Any suggestions? We've rebuilt the network from scratch, by the book, several times. We had these issues when using the Comcast provided gateway, and replaced it with our own and the issues still exist. Comcast has finally agreed to send someone out this weekend, but they keep saying their signal is within the accepatable limits. I'm willing to try just about anything at this point.
Start here: troubleshooting guide. If you still need help, please post your equipment details (make/model of your modem/gateway/router) and a screenshot of your signal levels and your error/event log. Thank you!