Visitor
•
2 Messages
Connection keeps dropping, fixes itself temporarily after resetting modem
I think I'm having the same issue as this one.
I recently moved to a new home. I had xfinity in my old place, and I never had problems with connectivity. I moved my whole setup, unchanged, to my new place, and now I keep losing internet connectivity every so often. I have to turn the modem off and on again, which fixes the issue for a few minutes/hours/a couple of days, but then the same thing happens. I feel pretty confident that my downstream setup (MikroTik router, Grandstream APs) isn't to blame - it's unchanged from my old house, and every time I've had this issue I've moved right next to an AP (which is wired to the router) to confirm.
I use a Motorola MB8611. The cable entering the house goes straight into the modem without any filters/splitters getting in the way.
Here's the event log from my modem:
Time Not Established
Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.1;
Time Not Established
Critical (3) UCD invalid or channel unusable;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.1;
19:54:16
Thu May 29 2025 Critical (3) UCD invalid or channel unusable;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.1;
10:06:09
Sun Jun 1 2025 Critical (3) Started Unicast Maintenance Ranging - No Response received - T3 time-out;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.1;
10:06:11
Sun Jun 1 2025 Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.1;
Time Not Established
Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.1;
Time Not Established
Critical (3) UCD invalid or channel unusable;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.1;
11:31:42
Sun Jun 1 2025 Critical (3) UCD invalid or channel unusable;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.1;
Time Not Established
Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.1;
Time Not Established
Critical (3) UCD invalid or channel unusable;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.1;
12:17:29
Tue Jun 3 2025 Critical (3) UCD invalid or channel unusable;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.1;
Time Not Established
Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.1;
Time Not Established
Critical (3) UCD invalid or channel unusable;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.1;
12:47:09
Tue Jun 3 2025 Critical (3) UCD invalid or channel unusable;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.1;
Time Not Established
Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.1;
Time Not Established
Critical (3) UCD invalid or channel unusable;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.1;
15:29:37
Thu Jun 5 2025 Critical (3) UCD invalid or channel unusable;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.1;
Time Not Established
Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.1;
Time Not Established
Critical (3) UCD invalid or channel unusable;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.1;
20:58:31
Sat Jun 7 2025 Critical (3) UCD invalid or channel unusable;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.1;
Time Not Established
Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.1;
Time Not Established
Critical (3) UCD invalid or channel unusable;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.1;
09:34:45
Sun Jun 8 2025 Critical (3) UCD invalid or channel unusable;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.1;
Time Not Established
Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.1;
Time Not Established
Critical (3) UCD invalid or channel unusable;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.1;
23:05:23
Wed Jun 11 2025 Critical (3) UCD invalid or channel unusable;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.1;
Time Not Established
Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.1;
Time Not Established
Critical (3) UCD invalid or channel unusable;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.1;
Time Not Established
Notice (6) Honoring MDD; IP provisioning mode = IPv6
08:37:42
Sat Jun 14 2025 Notice (6) DS profile assignment change. DS Chan ID: 32; Previous Profile: ; New Profile: 1 2 3.;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.1;
08:37:52
Sat Jun 14 2025 Critical (3) UCD invalid or channel unusable;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.1;
08:39:41
Sat Jun 14 2025 Notice (6) CM-STATUS message sent. Event Type Code: 24; Chan ID: 193; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: 0.;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.1;
Xfinity support only lets me talk to the chatbot, which tells me to restart everything and then assures me that everything is perfect. I'm not sure what to do next. Any help is greatly appreciated!
XfinityRay
Official Employee
•
3K Messages
26 days ago
Hi there, user_w1v7c6! Thanks for reaching out about your service and congratulations on your new place! We are happy to further help with your service and appreciate the steps you took as well as the modem logs. You did great trying to get this fixed! I agree this is most likely not the router but to rule that out, you would just test a connection wired to the modem to see if it
also drops. My bet is it would with what you are seeing.
Since you already checked the wires and equipment and reset everything, I will need to access your account from here. I can check the signals to your modem, the area, and go from there. This may be the outside line which a technician visit would fix.
Please send us a direct message with your full name and complete service address to “Xfinity Support”. To do so, click on the direct messaging icon located at the top right of this forums page.
Here's the detailed steps to direct message us:
• Click "Sign In" if necessary
• Click the "Direct Message” icon (upper right corner of this page)
• Click the "New message" (pencil and paper) icon
• Type "Xfinity Support" in the to line and select "Xfinity Support" from the drop-down list
• Type your message in the text area near the bottom of the window
• Press Enter to send your message
2
0