And I meant to add that, yes, it could be the nerves that come out of your lower back and go into the knee are not working right, or could be there's a pinch in a nerve within the knee joint, or even up in the hip joint, and that would prevent the right signals from getting to that knee. But that would be an equal possibility to the ones I listed in my first paragraph of the post I just made.
I'm not an expert in the nerves in the knee, but there is no question that your right knee is not supporting your weight properly. It could be from a little arthritis in that knee joint, it could be somehow the muscles in that knee have weakened, it could be you have a torn ligament there. It also could be part of your right-sided changes from the stroke.
Now, I have a wrecked-up back, and the nerves that go down into the legs don't always work like they should, I too have neuropathy, and on occasion I have had the experience of standing at the top of a stair, hanging onto the bannister, and when I put one of my legs down on the step, I know it's not going to support me. Very scary stuff. But it went away, so could have been almost anything that caused that. But I have been very careful with stairs after that, and usually I can only go up or down stairs with just one step at a time. I've always blamed it on my numb feet.
But since you are so much more active than me (no way I could play golf!), then obviously you need to see a doc about perhaps a brace or whatever it would take to help support that weak knee. A sports injury doc might be your best bet, they are so very good at diagnosing your sort of problem, they are always closely associated with physical therapy people, and they could order a brace, just everything you need. Or your own regular physicians could easily determine what is going on, a scan might reveal a joint problem, or just a regular exam of you. Sorry I couldn't offer more.