Our bodies are remarkably adaptive. If we do not feed on carbs, then it gets glucose from other places. Protein is the usual go-to and maybe you are eating more now. Are you losing weight, because the body will scavenge your own muscle tissue from you if it needs to.
The body also adjusts metabolic rate to compensate and conserve if it thinks it is being denied, I have seen it advised that either doing intermeiitent fasts or the occasional carb splurge can shock it into action again. But it must be a surprise otherwise it will learn to compensate for the new routine.
I don't know if LC diet stops working. I am 8 years into mine, and it still works reasonably well, but then again I have relaxed my goals since I started. I aim for an average daily result around 6.5 mmol/l which keeps me out of hypoland, and also avoids De Nile. I am eating more carbs now and my Insulin resistance and pancreas output is well tamed now.
what are your typical pre and 2hr readings doing? Are you being too strict with your goals? This is a marathon, not a sprint, so it is acceptable IMO to have more relaxed targets as one progresses. Try testing at 4hr after the meal to see if protein and fat is contributing.