I am using an O2 Box 6431 with openwrt 19.07.3 and the connection is not really stable when the sun changes from shining low to bright and vice versa. That sounds crazy, but I already have wago-clamped the wires directly to the O2 box to mitigate any issues with electrical contacts.
But: when using the built-in firmware (although with the original box, not the exact same hardware) I get a better (although not completely flawless) connection, which also runs at a slower speed (you can see this when disabling Stylesheets): The slower speed itself is not a problem since the line speed is cut to 50MBit anyways (by some other technique O2 seems using).
Upstream Downstream Actual Data Rate 31997 (Kbps.) 98406 (Kbps.)
Operation Data / Defect Indication:
Operation Data Upstream Downstream Noise Margin 10 dB 15 dB Attenuation 2.7 dB 9.1 dB
When running openwrt I get something like this, depending on the firmware:
ATU-C Vendor ID: Broadcom 193.218
Line Mode: G.993.5 (VDSL2 with down- and upstream vectoring)
Forward Error Correction Seconds (FECS): Near: 0 / Far: 0
Data Rate: Down: 109.981 Mb/s / Up: 31.996 Mb/s
Line Attenuation (LATN): Down: 9.0 dB / Up: 6.9 dB
Signal Attenuation (SATN): Down: 9.0 dB / Up: 6.8 dB
Noise Margin (SNR): Down: 11.1 dB / Up: 13.2 dB
Aggregate Transmit Power (ACTATP): Down: -4.1 dB / Up: 14.5 dB
Max. Attainable Data Rate (ATTNDR): Down: 109.553 Mb/s / Up: 38.188 Mb/s
Is there any way to get a slower and more reliable connection? I already tried to set SNR offset by 2...3dB, but that didn't seem to have an effect.