Are your clothes fitting the same?
Are you counting calories on your non fast days?

I can’t speak for anything than my own experience, but when I want to lose quicker I try for 4:3.
I also do very light exercise that adds up to my calories. So if I have 600 calories on a fast day I also get 600 calories of exercise. The difference is only in appetite for me. Say if I jumprope intense enough to break a sweat getting it all done in thirty minutes. I get hunger pangs. However if short bouts of calisthenics that I do all throughout the day over 16 hours add up to my fasting calories. Then the trick for me is getting good nutrition and good food, but counted out on non fasting days. I aim for a number of 6800 calories restricted over the whole week. Thats 2 lbs , but I also wind up getting food in my mouth without thinking sometimes. So generally by keeping a journal of meals on my phone app. I start to see how much snacking costs me in calories. I intake roughly 4000 calories when around other People. So I built that into my allowances. When figuring my targets.
Only other thing I can add from my experience is I believe my first experience on IF. Will not be at the same rate ad my second experience. Basically if I’ve already lost my first 30 pounds. The next 30lbs will be take much longer. So I taking a wild guess that your exercise activity has had successful impact and that 5:2 lifestyle may take longer to lose weight than someone whose been sedentary and trying to lose weight for the first time.

I can only point to something that may or may not be relevant to you. If a person has cut fat , not likes body builder , but like buying low fat foods? There is mention that if you need to eat just enough fat to trigger a response to burn or metabolize that fat, and that it also enables access to stored fat. I find it very odd that i need some fats from foods to release stored fat. Also that it doesnt apply to those who are sedentary.

Also, very early on (and possibly on another forum) many people who were starting at their ideal weight did report that their weight did not change much if at all. If you are already at your ideal weight and are super fit (ie; not much of a fat to muscle body composition change to be made) then you probably wont lose unless you get pretty draconian on your calorie intake on non-fastdays as well as fastdays.

The question is, if you’re already at your ideal weight and are super-fit and are getting all the health benefits of the fasting lifestyle on top – why would you want to live like that just to lose a couple of arbitrary pounds, which may show on the scales and nowhere else?

Sounds like a hiding to nothing to me. I think if I were in your shoes I’d just concentrate on making 5:2 a comfortable part of my longterm lifestyle and look forward to my wedding day.

Best of wishes for your big day.