Its perfectly possible to put weight on whilst eating a low carb diet ( I do it on and off lots ! ) , it also possible to do it whilst still being in ketosis ( I do that too ! )
If your metabolism is shot after years of low fat dieting , then the chances are that going LCHF alone will not create weight loss. What creates weight loss is that LCHF should cause you to stop binging on foods when not hungry and thus overall eating a much reduced calorie intake whilst at the same time keeping your metabolism working to burn off the fat.
One thing that one needs to appreciate is that overeating as a result of years of a deprivation cycle of low fat, causes the neural network in your brain linking you to eating to be quite strong.
( strong neural pathways for behaviour is why you can drive a car to a familiar destination without noticing, or why a woman subject to domestic abuse may choose a second partner who is also violent to her friends utter mystification)
I have found that its perfectly possible to still want to overeat -for example going into the kitchen and leaving it without eating something is very very hard for me to do, hungry or not, or deciding to eat something then eating more of it than necessary.
Because frankly that's what I've been doing for years and simply knowing I'm not hungry does not change the neural pathway in my brain that says " overeat" because that is what I do. The result of this is that I've been yo-yoing round the same 2 kilos for three months now. That probably won't change until I do manage to find a way to divert that neural pathway somewhere else.
The difference between the low fat way of life and this one, for me seems to be that I can actually react to the 2 kilos weight gain by cutting down again because the ketosis does mean that I am not feeling the actual hunger pangs, but the psychological behaviour remains. I am hoping that each time I win that particular battle I will gradually find it easier to do. I can see that that is the difference between my friend ( who lost all his excess weight easily ) and me. He can quite simply ignore food on the table if not hungry, I can't.
My guess would be that this " over eating " behaviour is still with you - and that is why you have started to eat slices of butter having been told butter is good, rather than simply eating normal portions enough to stop hunger.
good luck with the battle!