Thanks for using Syncfusion products.
We have validated the reported issue Ticks misposition in Slider inside the Tab, the cause of this problem is Tab component content will be initially rendered in the “display none” style.
In order to position the ticks and value the Slider needs to know the BoundingClientRect properties of the container element, but when an element is hidden these properties will be invalid.
But you can solve this issue by calling Reposition API inside Slider Created event. I have attached a sample showcasing solution below. Please get back to us if you need to further assistance on this.