Like the title says. Had the exact same issue 3 months ago almost to the day. Last time after waiting 2 weeks for a tech the internet went back to normal hours before he showed up and ended up just leaving without doing or checking anything. Here are my bonding channels up and down. Channels 2 and 3 are both not locked and have high power levels, same as last time. Restart my modem so many times already so that isn't a fix, maybe a bad modem?
You have RF signal / connection quality problems.
In a self troubleshooting effort to try to obtain better connectivity / more wiggle room, check to see if there are there any excess/unneeded coax cable splitters in the line leading to the modem that can be eliminated/re-configured. Any splitters that remain should be high quality and cable rated for 5-1002 MHz, bi-directional, and no gold colored garbage types like GE, RadioShack, RCA, Philips, Leviton, Magnavox, and Rocketfish from big box stores like Home Depot, Lowes, Target, Wal-Mart etc. Splitters should be swapped with known to be good / new ones to test
If there aren't any unneeded splitters that can be eliminated and if your coax wiring setup can't be reconfigured so that there is a single two way splitter connected directly off of the drop from the street/pole with one port feeding the modem and the other port feeding the rest of the house/equipment with additional splits as needed, and you've checked all the wiring and fittings for integrity and tightness and refresh them by taking them apart then check for and clean off any corrosion / oxidation on the center wire and put them back together again, then perhaps it's best to get the techs back out there to fix it properly.
I did all that last time this same issue came up, about 3 months ago. Luckily I'm getting a tech tomorrow morning. I'll update the fix if any tomorrow afternoon.
edit: They change the look of the forums today or did I change something by accident?
I had some sort of filter at the pole coming from my line. Tech removed it and clean up some other things he said, back to normal download speeds.