Try to achieve the following outcome: "between X% and Y%", with both input groups aligned on the same line.
This approach is successful when using standard form fields, however it encounters issues with input-group:
between
<div class="input-group d-inline-block" style="width: 5em;">
<input type="text" class="form-control" >
<div class="input-group-append">
<span class="input-group-text">%</span>
</div>
</div>
and
<div class="input-group d-inline-block" style="width: 5em;">
<input type="text" class="form-control" >
<div class="input-group-append">
<span class="input-group-text">%</span>
</div>
</div>