Cannot delete last item from repeater

I have a problem where I cannot delete the last repeater item in a blog post.

I believe it is the same issue that others have reported in the forum.

Some additional context:

• I added a repeater to an existing blog
• I used with the repeater in at least one blog post but most did not
• I have since updated the template but to my knowledge the id for the repeater didn't change
• New blog posts created after I updated the template behave as expected
• Posts that were already present always seem to have three items. Against each item I see:

Warning: Invalid argument supplied for foreach() in /var/sites/a/alexanderblackman.co.uk/public_html/perch/core/apps/content/PerchContent_Util.class.php on line 509

• If I delete any item this message disappears
• I can delete two repeater items but the last one persists

In my local development environment I have debug turned on and see what looks like to be the same error message:

Array
(
    [type] => 2
    [message] => Invalid argument supplied for foreach()
    [file] => /Applications/MAMP/htdocs/personal/portfolio/perch/core/apps/content/PerchContent_Util.class.php
    [line] => 509
)A

Diagnostic information

Perch: 3.0.14, PHP: 7.1.5, MySQL: mysqlnd 5.0.12-dev - 20150407 - $Id: b396954eeb2d1d9ed7902b8bae237b287f21ad9e $, with PDO
Server OS: Linux, cgi-fcgi
Installed apps: content (3.0.14), assets (3.0.14), categories (3.0.14), perch_blog (5.6.1), perch_forms (1.9.1), perch_kraken (1.1)
App runtimes: <?php $apps_list = array( 'perch_blog', 'perch_forms', ); ?>
PERCH_LOGINPATH: /perch
PERCH_PATH: /var/sites/a/alexanderblackman.co.uk/public_html/perch
PERCH_CORE: /var/sites/a/alexanderblackman.co.uk/public_html/perch/core
PERCH_RESFILEPATH: /var/sites/a/alexanderblackman.co.uk/public_html/assets
Image manipulation: GD
PHP limits: Max upload 100M, Max POST 100M, Memory: 128M, Total max file upload: 100M
F1: 3b606135b33e6a102526838f4152a807
Resource folder writeable: Yes
DOCUMENT_ROOT: /var/sites/a/alexanderblackman.co.uk/public_html
HTTP_HOST: alexanderblackman.co.uk
REQUEST_URI: /perch/core/settings/diagnostics/
SCRIPT_NAME: /perch/core/settings/diagnostics/index.php

post.html

<header class="container  pt-7">
    <div class="row">
        <div class="col-13  offset-1  col-sm-11  offset-sm-4  col-lg-10  offset-lg-5">
            <nav role="navigation" aria-label="breadcrumb">
                <ol class="breadcrumb  small">
                    <li class="breadcrumb-item"><a href="/">Home</a></li>
                    <li class="breadcrumb-item"><a href="/articles">Writing</a></li>
                    <li class="breadcrumb-item  active" aria-current="page"><perch:blog id="postTitle" type="text" label="Title" required="true" size="xl autowidth" order="1" /></li>
                </ol>
            </nav>
        </div>
    </div>
</header>

<article class="container  pb-7  c-post" role="main">
    <div class="row">
        <div class="col-13  offset-1  col-sm-11  offset-sm-4  col-lg-4  offset-lg-0  text-lg-right">
            <h1 class="h1"><perch:blog id="postTitle" type="text" label="Title" required="true" size="xl autowidth" order="1" /></h1>
            <p class="font-italic  font-weight-light  text-middle">
                <time datetime="<perch:blog id="postDateTime" type="date" label="Publish Date" native="true" divider-before="Publishing" />">
                    <perch:blog id="postDateTime" type="date" label="Publish Date" native="true" divider-before="Publishing" format="%e %B %Y" /> 
                </time>
            </p>
        </div>
        <div class="col-13  offset-1  col-sm-11  offset-sm-4  col-lg-10  offset-lg-1  mb-7" style="margin-top: 0.25em;">
            <div class="c-post">
                <perch:blog id="postDescHTML" type="textarea" label="Post" order="2" editor="simplemde" markdown="true" size="xxl autowidth" required="true" html="true" />
            </div>
            <perch:if exists="authorGivenName">
                <div class="text-right  mt-3  mb-7">
                    —&thinsp;<perch:blog id="authorGivenName" type="hidden" /> <perch:blog id="authorFamilyName" type="hidden" />
                </div>
            </perch:if>
            <perch:if exists="footnotes">
                <aside class="pt-7  mb-7  small" id="footnotes">
                    <h2 class="sr-only">By the way</h2>
                    <perch:repeater id="footnotes" label="By the way" order="3">
                        <perch:before><ol></perch:before>
                        <li id="footnote:<perch:blog id="perch_item_index" type="hidden" />" aria-label="footnote <perch:blog id="perch_item_index" type="hidden" />">
                            <perch:blog id="footnote-text" type="textarea" label="Note" markdown="true" html="true" size="m autowidth" /> <a href="#footnote-ref-<perch:blog id="perch_item_index" type="hidden" />" class="footnote-ref" aria-label="Back to content">↩</a>
                        </li>
                        <perch:after></ol></perch:after>
                    </perch:repeater>
                </aside>
            </perch:if>
        </div>
    </div>
</article>