I agree, it sounds like a faulty unit to me, I don't recall getting the same problems on mine.
Well, I haven't posted much about mine in a while, but over at OcUK there's been a lot of discussion on-going. After much perserverence babis3g and I may be now onto something causing the CRC errors. Time will tell, but looking promising at the moment. Every 12-24 hours I'm increasing the downstream sync rate as well as toggling between fastpath and an extremely light level of interleaving on the downstream (1ms 0INP and 3ms 0INP respectively). For the purpose of the tests I'm no longer looking at the FEC value, as I don't think/believe the Openreach DLM does anyway (it's such an unreliable value to consider in my opinion). I'm just considering CRC errors, error seconds, severe error seconds and any loss of sync.
Babis3g came up with the idea that the spectrum monitor might be causing the instability, so after I also noticed it running via telnet as 'spectrum' process, we've both killed it and so far results look good.
For a couple of hours during the early hours of the morning I tried 49Mbps on fastpath and the results were no spiking of CRC errors, just a standard trickle much like the HG612. Prior to that I had tested a 3ms delay with 0 INP (very light interleaving) at 49Mbps for quite a few hours and that yielded only a few CRC errors/error seconds (except for the FEC going wild, but I'm ignoring that).
Now I'm testing 54Mbps with 3ms delay at 0 INP. FEC out of control as expected, but after a few hours of uptime so far the CRC's are almost non-existent on the downstream despite the very light level of interleaving I've currently applied at the moment (almost fastpath). In the past I don't recall being able to apply such a low level of interleaving to this sync rate/SNRM.
DSL SettingsFirmware Version 2155DS bearer channel 0 configuration
Min_net_data_rate = 128 kbit/s
Max_net_data_rate = 54000 kbit/s
Max_interleaving_delay = 3 ms
INP_min = 0 symbols
near-end path0 fec: 6140400(19875159)
near-end path0 crc: 6(82)
near-end fec sec: 10313(18138)
near-end err sec: 4(67)
near-end ses sec: 0(0)
near-end los sec: 0(0)
near-end ua sec: 0(193)
far-end path0 fec: 471(477935)
far-end path0 crc: 0(1929)
far-end fec sec: 9(8188)
far-end err sec: 0(1447)
far-end ses sec: 0(0)
far-end los sec: 0(676)
far-end ua sec: 0(29479)
outDiscards=67
inDiscards=75
outBytes=876715439
inBytes=2412468665
outPkts=13642178
inPkts=15170414
fwVer= FwVer:5.5.1.126_B_A60901 HwVer:T14.F7_0.1
lineState=up
Opmode=ITU G.993.2(VDSL2)
SNRMarginDown=8.8 dB
AttenDown=10.2 dB
SNRMarginUp=9.3 dB
AttenUp=0.1 dB
DataRateDown=53999 kbps
DataRateUp=20000 kbps
WanListMode=0
FECDown=6140400
FECUp=471
CRCDown=6
CRCUp=0
HECDown=0
HECUp=0
ADSLUpTime= 3:02, 19 secs
ADSLActiveTime=0 min, 18 secs
PowerDown=11.1 dbm
PowerUp=6.4 dbm
AttainUp=28033
AttainDown=103020
ShowtimeStart=18
TotalStart=131
ATURANSIRev=0
ATUCANSIRev=0
ATURANSIStd=0
ATUCANSIStd=0
InterleaveDepth=573
AdslStandard=VDSL2
AdslType=ANNEX_B
mtenStandard=G.dmt.bisplus (Annex L)