Please have a look at this issue. I have full one-page simple html code to reproduce it. There are two modals - one on top, and one lower on the page. Input fields inside the modals. If you tap on input field, it scrolls to the very bottom so that I cannot see the input field. This issue occurs only with the bottom modal, not the top one. Using CHROME on ANDROID
Here's the code:
<!doctype html>
<html lang="en">
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
<!-- Bootstrap CSS -->
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/css/bootstrap.min.css" integrity="sha384-Gn5384xqQ1aoWXA+058RXPxPg6fy4IWvTNh0E263XmFcJlSAwiGgFAW/dAiS6JXm" crossorigin="anonymous">
<title>Hello, world!</title>
</head>
<body>
<h4>Hey</h4>
<button type="button" class="btn btn-primary" data-toggle="modal" data-target="#myModal1">
Open modal
</button>
<!-- The Modal -->
<div class="modal" id="myModal1">
<div class="modal-dialog">
<div class="modal-content">
<!-- Modal Header -->
<div class="modal-header">
<h4 class="modal-title">Modal Heading</h4>
<button type="button" class="close" data-dismiss="modal">×</button>
</div>
<!-- Modal body -->
<div class="modal-body">
Modal body..
<p>input</p>
<input type="text">
<p>input</p>
<input type="text">
<p>input</p>
<input type="text">
<p>input</p>
<input type="text">
<p>input</p>
<input type="text">
<p>input</p>
<input type="text">
<p>input</p>
<input type="text">
</div>
<!-- Modal footer -->
<div class="modal-footer">
<button type="button" class="btn btn-danger" data-dismiss="modal">Close</button>
</div>
</div>
</div>
</div>
<div style="height:1000px;"></div>
<div style="height:1000px;"></div>
<button type="button" class="btn btn-primary" data-toggle="modal" data-target="#myModal2">
Open modal
</button>
<!-- The Modal -->
<div class="modal" id="myModal2">
<div class="modal-dialog">
<div class="modal-content">
<!-- Modal Header -->
<div class="modal-header">
<h4 class="modal-title">Modal Heading</h4>
<button type="button" class="close" data-dismiss="modal">×</button>
</div>
<!-- Modal body -->
<div class="modal-body">
Modal body..
<p>input</p>
<input type="text">
<p>input</p>
<input type="text">
<p>input</p>
<input type="text">
<p>input</p>
<input type="text">
<p>input</p>
<input type="text">
<p>input</p>
<input type="text">
<p>input</p>
<input type="text">
</div>
<!-- Modal footer -->
<div class="modal-footer">
<button type="button" class="btn btn-danger" data-dismiss="modal">Close</button>
</div>
</div>
</div>
</div>
<!-- Optional JavaScript -->
<!-- jQuery first, then Popper.js, then Bootstrap JS -->
<script src="https://code.jquery.com/jquery-3.2.1.slim.min.js" integrity="sha384-KJ3o2DKtIkvYIK3UENzmM7KCkRr/rE9/Qpg6aAZGJwFDMVNA/GpGFF93hXpG5KkN" crossorigin="anonymous"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.12.9/umd/popper.min.js" integrity="sha384-ApNbgh9B+Y1QKtv3Rn7W3mgPxhU9K/ScQsAP7hUibX39j7fakFPskvXusvfa0b4Q" crossorigin="anonymous"></script>
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/js/bootstrap.min.js" integrity="sha384-JZR6Spejh4U02d8jOt6vLEHfe/JQGiRRSQQxSfFWpi1MquVdAyjUar5+76PVCmYl" crossorigin="anonymous"></script>
</body>
</html>