Slow VDSL speeds

It might be related more with your ISP line than with your device. Perhaps, try to keep it on your line and see if the speed goes up in a few days.

For information, here's my HH5a stats:

 OpenWrt 18.06.2, r7676-cddd7b4c77
 -----------------------------------------------------
root@OpenWrt:~# /etc/init.d/dsl_control status
ATU-C Vendor ID:                          Infineon 178.6
ATU-C System Vendor ID:                   45,43,49,20,74,65,6C,65
Chipset:                                  Lantiq-VRX200
Firmware Version:                         5.9.0.12.1.7
API Version:                              4.17.18.6
XTSE Capabilities:                        0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x2
Annex:                                    B
Line Mode:                                G.993.2 (VDSL2)
Profile:                                  17a
Line State:                               UP [0x801: showtime_tc_sync]
Forward Error Correction Seconds (FECS):  Near: 8318 / Far: 131808
Errored seconds (ES):                     Near: 32 / Far: 4899
Severely Errored Seconds (SES):           Near: 0 / Far: 1
Loss of Signal Seconds (LOSS):            Near: 0 / Far: 1690
Unavailable Seconds (UAS):                Near: 35 / Far: 35
Header Error Code Errors (HEC):           Near: 0 / Far: 0
Non Pre-emtive CRC errors (CRC_P):        Near: 132 / Far: 0
Pre-emtive CRC errors (CRCP_P):           Near: 0 / Far: 0
Power Management Mode:                    L0 - Synchronized
Latency [Interleave Delay]:               0.0 ms [Fast]   0.0 ms [Fast]
Data Rate:                                Down: 77.449 Mb/s / Up: 20.000 Mb/s
Line Attenuation (LATN):                  Down: 11.0 dB / Up: 9.1 dB
Signal Attenuation (SATN):                Down: 11.0 dB / Up: 9.0 dB
Noise Margin (SNR):                       Down: 6.0 dB / Up: 9.1 dB
Aggregate Transmit Power (ACTATP):        Down: -1.5 dB / Up: -1.4 dB
Max. Attainable Data Rate (ATTNDR):       Down: 77.447 Mb/s / Up: 25.899 Mb/s
Line Uptime Seconds:                      11983
Line Uptime:                              3h 19m 43s