I’ve seen this happen a lot. When I lost weight in school and went from fat to normal, most, to be fair, were pleased for me but a fat girl bullied me for my weight loss - and 3 other people said negative things around my weight loss.
i think it extends further than just physical issues such as weight though. - I think it can extend to e.g a formerly timid person becoming more confident etc. If a formerly timid person acts more confident, some people act very ‘patronisingly’ towards them or won’t accept their ‘no’ for example.
Just wanted to stress that this is definitely SOME people by no means all - majority of course are supportive. 😊