Blog slug doesn't contain a date

I've set up my blog and have created a page to show individual posts in Perch Runway. The problem is that they date isn't being prepended to the slug.

In Perch Runway settings I have:

Blog post page path: /blog/{postSlug}
Slug format: %Y-%m-%d-{postTitle}

My routes for the post display page are:

blog/[slug:s]
blog/[slug:s]/[preview:preview]

In the portion of diagnostics related to the blog I see:

perch_blog_update: 5.6
perch_blog_post_url: /blog/{postSlug}
perch_blog_site_name: Ovia Health Resources & Research
perch_blog_slug_format: %Y-%m-%d-{postTitle}

And yet, no date is being appended to the slug, so posts with the same name aren't unique.

My debug message is:

Debug Message - Perch Runway 3.1.1
[29] SELECT p.pagePath, pr.routePattern, pr.routeRegExp, p.pageTemplate, pr.routeOrder, s.settingValue AS siteOffline FROM perch3_pages p LEFT JOIN perch3_page_routes pr ON p.pageID=pr.pageID LEFT JOIN perch3_settings s ON s.settingID='siteOffline' UNION SELECT NULL AS pagePath, pr2.routePattern, pr2.routeRegExp, pr2.templatePath AS pageTemplate, pr2.routeOrder, NULL AS siteOffline FROM perch3_page_routes pr2 WHERE templateID!=0 ORDER BY routeOrder ASC, pagePath ASC
Matched route: blog/[slug:s]
Using master page: /templates/pages/blog/post.php
Page arguments:
Array
(
    [0] => /blog/infertility-and-patient-focused-care
    [s] => infertility-and-patient-focused-care
    [1] => infertility-and-patient-focused-care
)
[34] SELECT DISTINCT settingID, settingValue FROM perch3_settings WHERE userID=0
[1] SELECT SQL_CALC_FOUND_ROWS DISTINCT tbl.* FROM ( SELECT idx.itemID, main.*, idx2.indexValue as sortval FROM perch3_blog_index idx JOIN perch3_blog_posts main ON idx.itemID=main.postID AND idx.itemKey='postID' JOIN perch3_blog_index idx2 ON idx.itemID=idx2.itemID AND idx.itemKey='postID' AND idx2.indexKey='_id' WHERE 1=1 AND ((idx.indexKey='postSlug' AND idx.indexValue='infertility-and-patient-focused-care')) AND idx.itemID=idx2.itemID AND idx.itemKey=idx2.itemKey GROUP BY idx.itemID, idx2.indexValue, postID ) as tbl WHERE (postStatus='Published' AND postDateTime<='2018-05-16 19:18:00' ) GROUP BY itemID, sortval ORDER BY sortval ASC LIMIT 0, 10
[1] SELECT FOUND_ROWS() AS `count`
[1] Using template: /templates/blog/meta_head.html
[9] SELECT * FROM perch3_blog_authors ORDER BY authorFamilyName, authorGivenName ASC
[1] SELECT * FROM perch3_blog_sections ORDER BY sectionTitle ASC
[2] SELECT * FROM perch3_blogs ORDER BY blogTitle ASC
[34] SELECT DISTINCT settingID, settingValue FROM perch3_settings WHERE userID=0
[2] SELECT regionKey, regionHTML FROM perch3_content_regions WHERE regionPage='/blog/post' OR regionPage='*' ORDER BY regionPage DESC
[1] SELECT blogID FROM perch3_blogs WHERE blogSlug='blog' LIMIT 1
[1] SELECT SQL_CALC_FOUND_ROWS DISTINCT tbl.* FROM ( SELECT idx.itemID, main.*, idx2.indexValue as sortval FROM perch3_blog_index idx JOIN perch3_blog_posts main ON idx.itemID=main.postID AND idx.itemKey='postID' JOIN perch3_blog_index idx2 ON idx.itemID=idx2.itemID AND idx.itemKey='postID' AND idx2.indexKey='_id' WHERE 1=1 AND ((idx.indexKey='postSlug' AND idx.indexValue='infertility-and-patient-focused-care')) AND idx.itemID=idx2.itemID AND idx.itemKey=idx2.itemKey GROUP BY idx.itemID, idx2.indexValue, postID ) as tbl WHERE ( blogID=1 AND postStatus='Published' AND postDateTime<='2018-05-16 19:18:00' ) GROUP BY itemID, sortval ORDER BY sortval ASC LIMIT 0, 10
[1] SELECT FOUND_ROWS() AS `count`
[1] Using template: /templates/blog/post.html
Using sub-template: /templates/content/blocks/blog/text_block.html
Using sub-template: /templates/content/blocks/blog/text-over-3-links.html
Using sub-template: /templates/content/blocks/blog/pullquote.html
Using sub-template: /templates/content/blocks/blog/full-width-image.html

I tried adding a custom token, as in the Perch Runway Blog instructions, but that didn't help.

I feel like I'm missing something very obvious, but have been staring at it for far too long.