Thanks for your intervention with profile reset, it has worked.
Lower speed limit removal was required to achieve performance experienced prior to the landline failure.
Only question is, why openrenreach engineer failed to diagnose this and apply the fix?
Not surprised at all because they were not able to diagnose location of permanent ringing on landline fault in the first place. They rely on out of date methods and this goes to show their diagnostics need major overhaul. I sincerely hope someone in charge is able to spot the issue with customer experience side of things (deliberate need to inconvenience the customer before checking circuits in exchange). Of course, there is lot to learn about how to monitor equipment at exchange and to communicate with customer directly. That is why they have training to attend.
