Didn't someone else have a Fritzbox 7530 recently that was unstable and got it replaced which fixed everything?
It's a red herring. I have the same problem as he does (almost exactly) and so it's unlikely that BobC's issues were the same as mine because of the router. Plus, I've also tested using other routers (Broadcom/Lantiq-based) and it makes no difference.
Here is my Fritzbox graph from Sunday 2 weeks ago and from this Sunday (I believe the discrepancy in the times errors occur is due to BST change, but this could be a red herring, too). Is it that all my neighbours are on the Internet around the same time, their browsing resulting in cross-talk and so errors? Is it some kind of interreference (someone's equipment) that's on on Sundays - the times of errors suggesting that and also that it's a system on a timer like a boiler or hot water tank? Or is it a high resistant fault that has never been fixed because the line is difficult to access and it's performing within parameters (3 disconnections a day according to Plusnet and OR is acceptable). After the three drops today, preceded by an accumulation of errors, I have no errors on my Fritzbox counters at all despite being connected for 5 hours now.
So, in a nutshell, I have the same problem as BobC, including the fact that Min. effective data rate on my Fritzbox goes down to 3, whereas his is 6 kb/s.
BobC: what exchange are you connected to? Also, have you noticed that your 2.4GHz WiFi is also affected when these errors occur? Mine seems to be affected to the point where the router slows down big time, ping and jitter increase etc.
Another question to those reading the thread: what's the impact of an amateur radio station on VDSL signal?