This is expected if you are interrupting the current transition that is in progress. This also happens with the built in carousel controls.

I would also advise placing the next/previous controls outside of the carousel.

Internally the carousel uses the same next, prev, and setSlide methods.

I forgot to mention I had set the interval to 0 in my own code, to prevent the carousel from auto-sliding (updated the original codepen.)

The transition jumps occur when no transition is being interrupted.

If I move the next/previous buttons outside of the carousel, the transitions are smooth. See https://codepen.io/gmw-web/pen/pojZwNL?editors=1010.
I really hoped to avoid having to place the buttons outside the carousel, as this would break our layout. I try to use the carousel in a 'wizard' kind of way (a users needs to click through some steps, and in each step they need to click a specific target inside the slide).

I see that the built-in controls are also placed outside of the slides. although I don't really understand why placing the initiators of the action outside of the slide makes a difference if they still trigger the same methods/functionality in the end? 🤔

I looked into this a bit further, and noticed that some of the CSS classes (indicated with a red box in the image) are removed too soon, sometimes immediately. This appears to be what causes the transition to 'jump'.

This only occurs when the previous/next buttons are place inside the b-carousel-slide. When the buttons are placed outside of the carousel, the classes are removed only after the animation ends.

I played around with the codepen a little and found that if you tab to the prev or next buttons. then use enter to activate the button the correct transition plays. While click the button as you explained causes a glitchy jump in the transition.

I also played with using a setInterval to trigger the next/prev methods.
Using a delay of 250 somehow manages to make the transition play out correctly (95% of the time).

There's definitely something odd going on.

https://codepen.io/Hiws/pen/dyGbaMz