I've been doing 5:2 for about 12-18 months and have been really pleased with it. My routine is to eat sensibly on Mondays, Wednesdays and most of Fridays (no sweet things, no alcohol, minimal snacking, etc.), fast on Tuesdays and Thursdays, and be pretty relaxed about food/drink on Friday evenings, Saturday and Sunday. I also skip fasts when I'm travelling, for special events, etc. - maybe once per month on average.
I found that on this routine I lost weight slowly but consistently, I felt great, people complimented me on my weight loss, etc.
Over the summer, it went a bit to pot - I was away a lot and got out of the habit, and more or less gave up any kind of sensible food routine for 2 or even 3 months. Unsurprisingly, I put on a few kg, although less than I'd expected.
In early September I got back into the routine outlined above, and have been following it consistently since, so for about two months now. I'm just not seeing consistent weight loss as I did before. I feel like my eating patterns are the same, I'm exercises reasonably (about the same), but the weight just isn't shifting. What's going on?