Gigabit internet speed issues

Hi. We've recently upgraded from the 300Mb/s plan to the 1Gb/s option, and while we've seen a slight increase in speed (we're actually getting 300-400Mb/s now), we aren't getting anywhere near the rate we pay for.

I've followed most of the common troubleshooting guides, support has done 2 refreshes on their end (accompanied by me restarting our router/modem fairly often). I purchased an aftermarket modem (CM1150V) which is very much capable of handling the speed, and use a Netgear R700 for a router.

I have two computers connected via Ethernet that are able to transfer at roughly ~800-900Mb/s (through the router), so I am certain it is not a routing issue or problem with the computer itself. I have 32 locked downstream channels on the modem, however the event log generally has a lot of events and one of the downstream channels has a pretty poor correctable/uncorrectable ratio.

Again, to emphasize, I have already had multiple restarts (for several minutes) of both my modem and router, and have had Xfinity customer support perform refreshes on their end.

Attached is a snapshot of the modem information and some recent logs:

Time Priority Description
Mon Jun 29 11:34:40 2020 Warning (5) Dynamic Range Window violation
Mon Jun 29 11:34:40 2020 Warning (5) RNG-RSP CCAP Commanded Power Exceeds Value Corresponding to the Top of the DRW;CM-MAC=***********************;CM-QOS=1.1;CM-VER=3.1;
Sun Jun 28 13:46:30 2020 Notice (6) CM-STATUS message sent. Event Type Code: 3; Chan ID: N/A; DSID: �; MAC Addr: N/A; OFDM/OFDMA Profile ID: N/A.;CM-MAC=***********************;CMTS-MAC=***********************;CM-QOS=1.1;CM-VER=3.1;
Sun Jun 28 13:46:28 2020 Warning (5) Unicast DSID PSN startup error
Sun Jun 28 13:46:07 2020 Warning (5) Dynamic Range Window violation
Sun Jun 28 13:46:07 2020 Warning (5) RNG-RSP CCAP Commanded Power Exceeds Value Corresponding to the Top of the DRW;CM-MAC=***********************;CMTS-MAC=***********************;CM-QOS=1.1;CM-VER=3.1;
Sun Jun 28 13:46:07 2020 Warning (5) Dynamic Range Window violation
Sun Jun 28 13:46:07 2020 Warning (5) RNG-RSP CCAP Commanded Power Exceeds Value Corresponding to the Top of the DRW;CM-MAC=***********************;CMTS-MAC=***********************;CM-QOS=1.1;CM-VER=3.1;
Sun Jun 28 13:46:07 2020 Warning (5) Dynamic Range Window violation
Sun Jun 28 13:46:07 2020 Warning (5) RNG-RSP CCAP Commanded Power Exceeds Value Corresponding to the Top of the DRW;CM-MAC=***********************;CMTS-MAC=***********************;CM-QOS=1.1;CM-VER=3.1;
Sun Jun 28 13:45:56 2020 Notice (6) TLV-11 - unrecognized OID;CM-MAC=***********************;CMTS-MAC=***********************;CM-QOS=1.1;CM-VER=3.1;
Time Not Established Notice (6) Honoring MDD; IP provisioning mode = IPv6
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;