Bootstrap crossfade carousel - different data-interval issue - html

Question

I've got a Bootstrap crossfade carousel on my website with smooth fade transitions between the slides. I set an equal data-interval value for each slide to 5000 but the problem is that when I test the carousel in my browser the duration of each slide seems different per every one of them. The first slide's duration is the longest. The interval between the second and the third is very short, then between 3rd and 4th is longer again, and - between 4th and 5th is again very short, depsite the fact they have all the same value in the code.
I tried to tweak the interval values - no change. I tried different classes for interval - no change. I also tried to change fade transition CSS - no effect for interval of course. No matter what I do the duration varies per slide.
I tested it in 2 browsers. Same effect.
At least the fade transition looks ok. So where did I make a mistake in the intervals? What to do to make everything of the same duration?
The HTML for the crossfade carousel:
<div id="presentation-carousel" class="carousel slide carousel-fade" data-ride="carousel">
<div class="carousel-inner">
<div class="carousel-item active" data-interval="5000">
<img src="images\slideshow\slide1.jpg" class="d-block w-100" alt="...">
</div>
<div class="carousel-item" data-interval="5000">
<img src="images\slideshow\slide2.jpg" class="d-block w-100" alt="...">
</div>
<div class="carousel-item" data-interval="5000">
<img src="images\slideshow\slide3.jpg" class="d-block w-100" alt="...">
</div>
<div class="carousel-item" data-interval="5000">
<img src="images\slideshow\slide4.jpg" class="d-block w-100" alt="...">
</div>
<div class="carousel-item" data-interval="5000">
<img src="images\slideshow\slide5.jpg" class="d-block w-100" alt="...">
</div>
</div>
CSS for the carousel:
.carousel.carousel-fade .carousel-item {
display: block;
opacity: 0;
transition: opacity ease-in-out 3s;
}
.carousel.carousel-fade .carousel-item.active {
opacity: 1 !important;
transition: opacity ease-in-out 3s;
}