Interesting - this looks like Beransa[1] (Librela) which is a monthly injection for canines that have osteoarthritis. My dog did not have any noticeable changes to pain after using this for 2 months so I've decided to take him off of it.
One theory is that the immune system eventually starts attacking the monoclonal antibody med itself, another is that as in humans, the OA progression might accelerate under the drug.
I actually (anecdotally) heard a similar issue with Pentosan that it stops working after 12-24 months due to the immune system so you have to "time it" at an appropriate time in a dog's life. To be blunt, by appropriate I mean you'd want to start using it 12-24 before the dog is expected to pass and not at the first sign of osteoarthritis.
My dog's been on it since last October, and it's made a big difference for him. Sorry to hear that it didn't help yours.
I've been wondering how long it would be before something similar was available for humans.
On the bright side, I also have mine on Pentosan which did have a noticeable difference for him so that's great