You may want to cut back on those a little bit...could be having the opposite effect of what you think it will. With walking, consistency is the key not necessarily how long at a single time you do. IMO, walking 5 days for 30 minutes will give you better results than walking 3 hours at once and not walking at all the other days.
So basically stubborn weight loss can be attributed to a few things.
1) You are eating too much. Do you know what your TDEE is? What your BMR is? I'd recommend this one...it's a carb cycling calculator but it's been pretty spot on for my usage just for determining calories.
2) You aren't eating enough. Personally anything more than a 500 calorie deficit food wise causes my weight loss to stall. Highly recommend going no more than a 500 calorie deficit from your TDEE.
3) Insulin Resistance. Your focus should be on improving glucose sensitivity. This helps you burn fat better 24 hours a day, 7 days a week, 365 days a year. For me there are a few things I use that work well. Consistent walking is the easiest thing to do. Simply repetitive movement of the big lower body muscles helps drive glucose out of the bloodstream without insulin. I take berberine and Alpha Lipoic Acid in combo in the morning as that also has shown to have a great effect on blood sugar levels. I take Cinnulin PF before dinner(you could also just sprinkle some cinnamon in your food or a shake) which is very good at lowering blood sugar levels as the active ingredient in cinnamon has a similar structure to insulin and the body uses it as an insulin mimetic. Before bed I take 1 TBSP of ACV in a glass of water. That helps keep blood sugar levels stable throughout the night and helps keep them lower. And of course I do 5:2 fasting where 2 days a week I fast for 32-40 hours, which has been shown to be outstanding for improving insulin sensitivity. Is all this overkill? Probably, but my default state my whole life is some level of insulin resistant so I have to fight to overcome that. Any or all of these will help in that way.
4) Carb Cycling - it works exceptionally well. I do 4 lower carb days, 2 high and 1 medium and kind of mix them up every week to keep my body guessing. Typically a high carb day will always be leg day but the others I mix up. The 2 fasting days count as low carb obviously since I don't eat anything haha.
5) Overtraining/lack of sleep - sometimes you need to give your body a rest. Overnight heart rate is a good indicator of this...if it's 5-7+ BPM higher than normal for more than a day you are in an overtrained state and your body needs a rest. Additionally lack of sleep is an absolute killer for losing weight. It's among the most stressful things your body can have done to it and the hormonal state will reflect it. High cortisol, low T, high ghrelin, low leptin. Basically the worst possible environment for fat loss. Prioritize your sleep and you will see much better results.
Since mid January I am down 32 lbs as of today, and thst included a 2-3 week period right after I dropped the first 10ish pounds where I had to make some adjustments to kick start more weight loss becauee I was stuck in a 3-4 lb range back and forth over that period. Mix of resistance training, walking, carb cycling(with proper calorie levels), diet and focusing on insulin resistance/blood sugar levels.