Drop down scroll not responding in mbsc-popup

In mbsc-popup we are showing a dropdown (using mat-select) but the mat-options are not scrollable using the mouse scroller, we are able to scroll using the scroll bar on right side.

Note: mbsc-popup is scrollable but not mat-select options
Version: mobiscroll-angular-5.21.0

Below is the code for the dropdown in mbsc-popup.

<mat-form-field [appearance]=“‘fill’”>
< mat-label>Test label</ mat-label>
< mat-select multiple >
< mat-optgroup>
< mat-option>1</ mat-option>
< mat-option>2</ mat-option>
< mat-option>3</ mat-option>
< mat-option>4</ mat-option>
< mat-option>5</ mat-option>
< mat-option>6</ mat-option>
< mat-option>7</ mat-option>
< mat-option>8</ mat-option>
< mat-option>9</ mat-option>
< mat-option>10< /mat-option>
< mat-option>11</ mat-option>
< mat-option>12</ mat-option>
< mat-option>13</ mat-option>
< mat-option>14</ mat-option>
< mat-option>15</ mat-option>
< mat-option>16</ mat-option>
< mat-option>17</ mat-option>
< mat-option>18</ mat-option>
</ mat-optgroup>

the value of the scrollLock option - which disables page scrolling, if the content of the popup is not scrollable - defaults to true. Try setting it to false and let me know if it solves the issue.