After years of troubleshooting and dozens of techs coming to my house, I was finally able to get the diagnosis I had suspected. They found a problem with the pedestal and some damaged fiber optic line in the run from the node. They say, now, that they have fixed the problem.
I think since you have an established 2 1/2 year history of this problem and the provider has finally acknowledged the problem was on their side, you should
aggressively pursue some compensation for your troubles and lack of consistent, promised service.
I don't know how much you pay for your service, but after 2 1/2 years, I am sure it was not chump change.