Shepherd adds flip and shift to default options, then does a deep merge with any other options passed in. Flip and autoPlacement are not compatible so adding autoPlacement to floatingUIOptions.middleware just causes errors.

I tried not passing in a placement so shouldCenter is true, but there are side effects in other parts of the code that block floating UI all together.

You could check for something like :on "auto" to skip adding flip. autoPlacement doesn't need a placement so you can skip options.placement = attachToOptions.on; too.

https://github.com/shepherd-pro/shepherd/blob/master/src/js/utils/floating-ui.js#L169