I can give one example of change.
When I first joined plusnet, if I raised an issue, the forum staff were able to resolve it personally, they had the power to do that.
When they got replaced with members of another team (as the department got dissolved), that new team instead of taking ownership of problems would simply pass on the problem to the standard support staff with a request to treat the problem with a bit higher urgency. They seemed to not have the power to fix things themselves.
Its also around that time things like the exchange status and other stuff that was maintained by that original team stopped been updated.
Plusnet when I joined them did have problems, but they were more like annoyances then big issues, it was generally congestion free, and was competent staff manning the forums able to fix almost everything.
Fast forward to now and various alarming things have happened.
They gone from testing ipv6 to now not having any foreseeable capability to launch it (as the new gateways seem to not support it).
The staff manning the forums are not as useful as the first bunch were, bob seems to be the only staff member left who is genuinely frustrated with problems, but he is just one guy, he cannot perform miracles.
As the process of migrating from ag to bgn gateways started, performance problems appeared, and since then they have never been fully resolved.
They have reverted to 40/2 as their mainstream FTTC product, when prior to that was 40/10 and 40/20.
Publicly available information has gradually been removed.
24/7 support became daytime and evening support.
Tickets have been replaced with live chat an inferior system.
Plusnet has basically been transformed into a mass market isp by its management (who someone else has pointed out are not even on plusnet's payroll but BT instead) which is targeting the market segment below BT retail.