Tags vanish from blog post after a little while

I've noticed this issue a few times in the past, but thought I was going mad.

I wrote this blog post today, filled in the metadata and made it live. Immediately after going live I checked the post and the tags were displaying on the post.

I subsequently went back to look at the post a little while later, and the tags aren't displaying any more.

The tags are still listed under the Meta and Social tab in the post admin.

If I look in the database perch_blog_posts has the tags in the postTags field, but there's no entry with that postId in perch_blog_posts_to_tags.

The only custom thing I'm doing with the tags is running them through perch_blog_custom to turn them into links:

perch_blog_custom([
        'template' => 'post.html',
        'filter' => 'postSlug',
        'match' => 'eq',
        'value' => perch_get('s'),
        'count' => 1,
        'each' => function($item) {
            $item['tags'] = perch_blog_post_tags($item['postSlug'], 'post_tag_link.html', true);
            return $item;
        },
    ]);

In the past I've fixed this by just re-saving the post, but I'd like to try and get to the bottom of this if possible. Now that I'm blogging more it's a bit of a pain.

G.

Diagnostic info

    Perch Runway: 3.1.1
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    <?php
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        'perch_blog',
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