Great question, Doughnut! I have similar ones myself. The mysteries of the human body .... Here are a few ideas, FWTW.
1. We change over time. How old are you? I gather that older people require fewer calories than younger. (This is a message I don't like to hear as I am 54 so I have developed selective hearing when it's mentioned. People also weigh in with stuff about the menopause which I also ignore as I am going strong.) (Sorry, slight digression there. It gets me going every time.)
2. For me, it seems that formal exercise is central to losing weight. Without it, I just don't. You could be the same. So however active I am (for example, in the school holidays when it's more difficult to get to the gymn I always fall off the wagon). I've found I need weights, cardio and stretching.
3. What about the balance and quality of stuff in your diet (protein, fats, complex carbs, water)? For example, 1300 calories of doughnuts and dumplings are probably not as good for you as 1300 calories of Shredded Wheat, skimmed milk, berries, lentils, salmon and broccoli.
4. Sleep. This is central for me. 'Research has shown' (can't remember which but someone will know) that lack of sufficient sleep affects weight loss success. Yes, you might be able to stagger along quite well with 7.5 hours sleep but your body might prefer 8 and show you that.
5. Stress (possibly linked to the above). I think too much of this produces a hormone called cortisol which also has bad effects on weight loss success. You may be an extremely chilled person but we've just gone through the Christmas and New Year period to find ourselves in the grip of a winter not-so-wonderland. I read in another of your posts that you work in Worcestershire which is closed at present. Bit stressful, that. It would certainly jam me up, rather like travel and being away from home does. Even though, at the time, I think I'm coping rather well.
6. Just the cold weather. Your body might be trying to be sensible and conserving fat just in case this cold period goes on for a lot longer and you find yourself stuck in a snowdrift.
Very good luck, Doughnut. Stick at it and keep coming here.