I'm using the default theme:  "@progress/kendo-theme-default": "4.18.2" with some custom overrides.

The generated CSS has the following incorrect rule (because of the unitless zero, see https://www.w3.org/TR/css3-values/#calc-type-checking ):

.k-combobox .k-dropdown-wrap .k-clear-value {
	calc( calc( 1.2em + 8px) + 0 + 6px)
}

This rules comes from the following scss:

$picker-icon-offset: calc( #{$picker-select-calc-size} + #{$picker-select-border-width}  + #{$input-icon-offset}) !default; 

The unitless zero comes from this value:

$picker-select-border-width: 0 !default;

As a result, the "X" in a combobox overlaps the value.