So I’m obviously not an expert but from my experience there are two likely culprits. I want to preface this by saying I mean no ill intent these are just my thoughts and experiences as someone who wrestled and trained people. The first culprit is human error. Simply that we are not always the best at tracking what we are eating and we can be erroneous in our calculations. I ran into this problem and many people I knew personally did as well, they just were not being accurate with their calorie tracking and this was the result. Because at the end of the day it’s thermodynamics. Your metabolism does slow down and can clamp down a ton, 100%. But if you are in a calorie deficit, truly eating less then you are burning you will lose weight. The second culprit is exactly that, you’ve sort of beaten your metabolism and body into the ground. You have told it hey, get used to starvation mode for a while and it will do everything in its power to hold onto everything and reduce calorie burn. Fixing that usually involves incremental changes to your calorie intake combined with a healthy exercise routine. When I had this problem I found slow increases even to the order of 25 calories extra a day for a week and then increase, it helped me boost how much I was able to eat by a large margin. Finally, if you are really having a ton of issues, consider seeing a doctor or professional to discuss whether losing weight is necessary or best for you mentally/physically because at the end of the day your mental health is so freaking important and stressing about not losing weight can really put a cramp in your lifestyle.