It took about 2 months and 5 visits to get my outages fixed. I also had to get some of my neighbors to report the outages.
Bunch of
UCD invalid or channel unusable and SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing
have you grabbed an extension cord and tried connecting the modem outside at the drop for awhile?
i hear you that your neighbor has the same issue. but if youre in. say a development by the same builder, or were all part of a comcast upgrade at roughly the same time ..
and well… you both recently upgraded to 1.2(?) because that would be the latter case
after my gig upgrade and a few tech visits i ended up finding a splitter that only goes up to 800mhz or so (if that) inside a wallplate.
TLDR:
you might have a 5-1000mhz splitter. thats widely used by comcast still.
MORE:
OFDM is 1008mhz or so and you wouldnt notice the problem under, or maybe just UP TO gigabyte speeds (eg: downgrading to 500mb might mysteriously “fix” it).
but you WILL notice this at 1.2gb.
spectrum is future proofing and using 5-2500mhz splitters
ANECODTAL:
my modem locked with the 800mhz splitter, but it dropped , cycled and had horrible upload speeds.
techs never tried or thought of this . the final boss tech took photos and even took the splitter back to show his boss. i guess multiple units had tickets after the gig upgrade and they had an “aha” moment.
TECHNICAL:
i would expect something more like multiplexing errors in this situation. forgive me because im 20 years out of the game (was an RF/install tech on analog CATV , and cable modems when those were brand new to Charter) and had to look it up but i think docsis 3.1 is dependent on 957–1151 MHz or 1008–1152 MHz
its that 1008+mhz where now your splitter is acting like a 5-1000mhz filter.
its not perfect like okay maybe 4-1003mhz gets through the filter maybe even more permissive if its a cheap one. but thats NOT a clean signal for that frequency band its more like bleed-through.
sort of similar to traps (the little barrels theyd screw onto your line to block you from getting pay channels in the olden days) and how you STILL could sort of see and hear. a little bit of what was going on on cinemax at 3am and at least get the IDEA. :>
or, plugging your modem into your dmarc/outside box for a little bit would also confirm or deny this
i think my inside wiring was done no earlier than 1991 , but maybe redone once since then and it looked pretty good but i found this on the back of a wallplate , just yesterday:
- expires in 6 months
the easiest thing to do is check it at the box and then if nothing else thats ammo for dealing with customer service “look, i connected at the drop and have the same issue its NOT my inside wiring.”
everything from that point back is their problem and they owe you bill credits until its fixed, so get the proof and go back with it.
in my case my modem worked perfectly at the drop :D so i unfortunately had some digging to do
its not practical to suggest someone on the internet go ripping open all their wall plates and checking every inch of inside wire or maybe even running a new one. unless it passes the drop test, and then yeah, thats what needs to be done.
but plugging into the drop will 100% prove whose problem this is. youre california so thats also good ammo for a PUC complaint, that you did that and proved its not your inside wiring and now theyre refusing to deal with it. maybe that will get it to the right person on comcasts end faster when they review it.