**This is just for fun / speculation as the issue is under investigation by Enhanced Support / OpenReach / BT Wholesale**
Two sites on Zen and BT, FTTC, IPs 184.108.40.206 & 220.127.116.11, sites are about 150 meters apart. Both have suffered 5-20% packet loss for around 6 weeks. Copper status and VDSL statistics are great, great speeds, no drops, few errors etc. Many many Pair Quality Tests have been conducted 😉
Logging shows a very noticeable improvement in packet loss in the wee small hours (daily):
Lift and shift has been carried out for want of a better idea.
Running traceroute and pathping, the loss appears to occur on the last hop to the premises - ie from outside you can ping all the hops except the fault premises without loss
Engineers have also ruled out CPE, hot VP, electrical interference (REIN, SHINE).
I've now got a fiver on 'broken BRAS', but I know diddly squat about VDSL delivery, so would love to hear other wild guesses. Have at it!