Next button disabled in Select on Ionic iOS

I am building a Ionic app. I have 4 Select boxes in the form and have assigned tabindexes to them in sequence. The data is populated dynamically for all Select’s based on ng-change.
Code is like below.

<div class="col">
      <div class="row">
          <div tabindex="1">
              Pickup Date
                 <select id="pdSelect" ng-options="pdate in pickupDates" ng-change="dofirst()">
                 </select> 
          </div>
          <div tabindex="2">
              Pickup Time
                 <select id="ptSelect" ng-options="ptime in pickupTimes"  ng-change="dosecond()">
                 </select> 
          </div>
      </div>
      <div class="row">
          <div tabindex="3">
              Dropoff Date
                 <select id="ddSelect" ng-options="ddate in DeliveryDates" ng-change="dothird()">
                 </select> 
          </div>
          <div tabindex="4">
              Dropoff Time
                 <select id="dtSelect" ng-options="dtime in DeliveryTimes"  ng-change="dofourth()">
                 </select> 
          </div>
      </div>
</div>

When I run it in ios emulator or device, the NEXT ( ‘>’ ) button is disabled when we click Pickup Time. Normally it should be enabled and go to Dropoff Date.

Also, the NEXT ( ‘>’ ) button is disabled when we click Dropoff Date.

Any suggestions on how to enable NEXT ( ‘>’ ) button please.

Below are the images.
image
image

Can someone from Ionic team help on this please