Number of items per page sometimes 2

I want only one item per page so I use this:

            <carousel ref="carousel" :perPage="1">
                <slide>
                    <...></....>
                </slide>
                <slide>
                    <...></....>
                </slide>
                <slide>
                    <...></....>
                </slide>
                <slide>
                    <...></....>
                </slide>
            </carousel>

When I reload a page, sometimes 2, sometimes 1 item is shown.