Your IP profile of 29036K suggests a sync speed of 29999 K.
It may be pure coincidence, but that does look suspiciously like a 30Mb sync speed cap to me.
(39999 K is the sync speed for the 40Mb service - for those whose connections are physically able to connect at full speed).
The question has to be, what is currently restricting your sync speed that wasn't previously restricting it.
If we assume you were indeed genuinely achieving 35Mb+ throughput for a reasonably prolonged period, it may suggest that DLM has set your sync profile at a lower level due to the previous connection issue(s).
This may resolve itself over a prolonged period of a continuous & relatively error free connection.
However, we are aware that the sync speed profile can occasionally end up "stuck" indefinitely at too low a level, especially following repair work and/or replacement of a defective modem.
Currently this can only be reset via an engineer's site visit when he/she has to contact the fibre centre & request it.
Any requests directly from end users or ISPs are apparently politely refused.
I have personally suffered from a problematic connection for 6 months that was more or less perfect for the first month.
Modems have been replaced unnecessarily, various repair works have been carried out, my connection is now supposedly at the best it could ever be, yet I cannot currently sync over 30Mb.
Not all engineers will request such a reset. Some even refuse to request it (at least 2 engineers in my case).
One engineer did try his hardest to get it reset, but the fibre centre refused, on the basis that my connection could only have ever supported a sync speed of 24Mb maximum.
That engineer actually had in his hand a number of dated printouts of my connection achieving 33Mb throughput, suggesting a sync speed of around 35Mb.
Some of the printouts were from BT's own speed tests.
One engineer actually contacted my ISP to query why I was looking for throughput speeds of more than 20Mb when he was only seeing 22Mb at the cabinet.
He was politely informed by my ISP that I had a FTTC connection with an "up to" 40Mb sync speed.
He was one of the engineers that refused to request a reset.
Slowly pulling my hair out now as you can see from my Speed Sig what I was normally getting until the frigging Modem packed up and had to be changed.
I know what you mean.
Why else do you think my forum name is BALD
All I can suggest is that you keep on at your ISP to request a specialist engineer who has actually received the relevant training, to visit your home in order to request a reset (at no cost to yourself).
Unfortunately, not all the engineers who are sent to investigate/repair FTTC faults have received relevant training.
Please don't directly blame them for any failings as it is NOT ALWAYS THEIR FAULT
I have to assume that you have already carried out the usual tests of disconnecting any internal wiring (extensions etc.) to eliminate any internal issues that would undoubtedly end up in you having to foot the bill for the engineer's visit.
No definitive answers I'm afraid, but perhaps food for thought?