The problem here is: the ngx mask and angular material datepicker combined, they cannot be combined!
It is a limitation of Angular
<div class="form-group">
<label class="control-label col-lg-2 text-right">Birthday</label>
<div class="col-lg-4">
<input type="text" class="form-control" formControlName="birthday" placeholder="MM/DD/YYYY" mask="00/00/0000" autocomplete="off" bsDatepicker>
</div>
</div>