How is it possible that same lines of code work differently from time to time?

I've already noticed that simple multiplication in javascript sometimes gives incorrect results. By incorrect I don't mean floating value problem (2.999999 instead of 3) I mean absolutely incorrect result i.e. 2.6581 instead of 44.919283.

I tried to recreate the situation in short lines of code but I didn't manage to do it. I only notice these errors in my whole program.

For example I have these lines:

 console.log('myHighestBuy = ' + myHighestBuy);
 console.log('theirLowestSell = ' + theirLowestSell);

 if ((theirLowestSell * 0.85) > myHighestBuy){

   console.log('If condition is true');
   offerDeal(name, theirLowestSell, MarketPrice, myHighestBuy)

 } else {

   console.log('Not calling offerDeal()');

 }

What I have noticed, that once it has called offerDeal() function despite the fact it shouldn't had to.

Correct case console logs:

myHighestBuy = 16.22
theirLowestSell = 27.78
Not calling offerDeal()

But once I had in my console this:

myHighestBuy = 16.22
theirLowestSell = 27.78
If condition is true

Why is it possible? Is it if condition failure or multiplication error?