next prev arrows are not shown

Using <%= this.Scheduler.Render()%> on client side (.aspx) files shows the Scheduler but without the date selection arrows on the upper most bar of the Scheduler. Hoovering over the assumed position of the arrows changes the mouse behavior anf the selected date is changed accordingly, but the arrows are still not visible. What is the problem?

this is not happening in our samples, so the issue might be related to styles applied to the page.
Please check the arrow elements with Inspector from a browser dev tools, there might be some css settings that hides buttons