@Becky1984 - If you just Google "weight loss not a straight line" you will find lots and lots and lots on this.
To be honest, we've probably all, at one time or another quipped, "I just need to look at that and I gain 2kg (or whatever). That
short term gain is usually just water retention, often associated with carbs, or simple bulk.
There are many, many things influence our day to day weight - even when stable.
I'm pretty slight, but even though my weight has been very stable for years, on a day to day basis, I can very by up to 2kg. I can be lighter if dehydrated, or if I've eaten lightly (small meals, not necessarily LC/low cal or whatever), for example, and I can weigh more if I've had a great big meal - even if keto, if I'm constipated (sorry, TMI) or if I'm retaining water for whatever reason.
If you are sticking to your successful way of eating, then stick with it. You may experience quite a downship one day.
All of the foregoing is assuming you are eating adequately and not putting yourself into starvation mode, which is extremely unhelpful.
In your shoes, I might be inclined to keep a strict food diary of everything I ate and drank for a couple of weeks, just to ensure there isn't any carb creep happening.
Well done on that very significant weight loss. I hope you feel better for it.