High error count on Lantiq with ADSL

I'm using an O2 6431 (Arcadyan VGV7510KW22) on a Deutsche Telekom ADSL line. I noticed a very high "Errored seconds (ES)" count. Around 50 per minute and an also steadily increasing "Header Error Code Errors (HEC)" with around 20 per minute.

First I thought it could be some kind of interference from the internal Wifi and it was gone for a while. A few days later it was there again.

I read something about problems with the internal Switch and I thought this could be the cause and I disabled "Enable VLAN functionality". And again it was gone for a while, but is now back again.

Then I switched over to my second LEDE device. An TP-Link WD9980. And there's exactly the same behaviour.

Is this normal? What exactly is "Header Errors Code Errors"? Is this related to ADSL?

I have this ADSL connection until 26. April. Then it will be upgraded to VDSL50. If it is related to my ADSL connection and you want me to try some possible fixes this has to happen before 26th

Thanks in advance

Christopher

Firmware Version:

LEDE Reboot 17.01.0 r3205-59508e3 / LuCI lede-17.01 branch (git-17.051.53299-a100738)

DSL Status:

Status: UP
Line State: showtime_tc_sync [0x801]
Line Mode: G.992.5 (ADSL2+)
Annex: B
Profile: 
Data Rate: 11.098 Mb/s / 1.167 Mb/s
Max. Attainable Data Rate (ATTNDR): 11.056 Mb/s / 1.484 Mb/s
Latency: 0.25 ms / 0.25 ms
Line Attenuation (LATN): 10.8 dB / 3.4 dB
Signal Attenuation (SATN): 13.3 dB / 3.2 dB
Noise Margin (SNR): 6.3 dB / 17.4 dB
Aggregate Transmit Power(ACTATP): 12.3 dB / 12.6 dB
Forward Error Correction Seconds (FECS): 0 / 0
Errored seconds (ES): 683 / 0
Severely Errored Seconds (SES): 0 / 0
Loss of Signal Seconds (LOSS): 0 / 12
Unavailable Seconds (UAS): 22 / 22
Header Error Code Errors (HEC): 324 / 0
Non Pre-emtive CRC errors (CRC_P): 0 / 0
Pre-emtive CRC errors (CRCP_P): 0 / 0
Line Uptime: 12m 57s
ATU-C System Vendor ID: Infineon 113.190
Power Management Mode: L0 - Synchronized

/etc/config/network
https://gist.github.com/CReimer/fba30e9749cbbaac4f3bef2c078fd98a

That's normal behaviour on bad DSL connections. You can Google around for some improvements for your infrastructure, but don't expect big changes.
Anyway, if the internet bandwidth is high enough, there's nothing to be worried about.