Images uploaded to default S3 bucket not processed

Perch Runway is having problems processing some jpgs uploaded to the default (S3) bucket but not others.

Here are 2 images from the same batch: 1) https://www.dropbox.com/s/x0y4pzela7zb9e7/Southern%20Int%204.jpg?dl=0 2) https://www.dropbox.com/s/0ud72qhzf297u7b/Southern%20Int%205.jpg?dl=0

Both images have been resized / reduced to 72dpi & batch saved from Photoshop (saved as jpg, quality 10).

When uploaded directly into the assets panel (not using a template) & default S3 bucket ('assets-cdn') selected, the first image uploads fine & a thumbnail is created for it. The second image gets uploaded ok (the file is there on the download link after it says 'Successfully updated' ), but it doesn't get processed, i.e. no thumbnail is generated, and when you re-open the image in the assets panel, the download link is gone.

I also tried duplicating the second image, renaming it then uploading again but same problem. It seems to get processed fine when I uploaded it to another install of Perch (normal / non S3) and if I 'save for web' out of photoshop as opposed to 'save as jpg', it also uploads and gets processed fine. That's fine for me to do in this situation but not so easy for the client.

Any ideas why the 2nd image (& others) aren't being processed? Anyone else experience these issues with the S3 implementation?

Perch Runway: 3.0.14
Production mode: Production (100)
Installed apps: content (3.0.14), assets (3.0.14), categories (3.0.14), perch_blog (5.6.1), perch_forms (1.10)
DB driver: PDO
DB tables: perch2_backup_plans (0), perch2_backup_resources (0), perch2_backup_runs (0), perch2_blog_authors (5), perch2_blog_comments (0), perch2_blog_index (856), perch2_blog_posts (17), perch2_blog_posts_to_tags (51), perch2_blog_sections (1), perch2_blog_tags (48), perch2_blog_webmention_queue (0), perch2_blogs (1), perch2_categories (102), perch2_category_counts (5), perch2_category_sets (5), perch2_collection_index (72837), perch2_collection_items (459), perch2_collection_revisions (60), perch2_collections (2), perch2_content_index (9616), perch2_content_items (345), perch2_content_locks (1), perch2_content_regions (73), perch2_forms (3), perch2_forms_responses (997), perch2_menu_items (12), perch2_navigation (1), perch2_navigation_pages (6), perch2_page_routes (10), perch2_page_templates (21), perch2_pages (44), perch2_resource_log (39224), perch2_resource_tags (172), perch2_resources (6328), perch2_resources_to_tags (1023), perch2_settings (35), perch2_user_passwords (7), perch2_user_privileges (43), perch2_user_role_buckets (4), perch2_user_role_privileges (41), perch2_user_roles (3), perch2_users (10)
Users: 10
App runtimes:
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Scheduled tasks for perch_blog: delete_spam_comments (1440 mins), publish_posts (1 mins), process_webmentions (1 mins)
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PERCH_DEVELOPMENT: 10
PERCH_STAGING: 50
PERCH_PRODUCTION: 100
PERCH_DB_DATABASE: hiddenir_db
PERCH_DB_USERNAME: hiddenir_user
PERCH_PRODUCTION_MODE: 100
PERCH_DB_SERVER: localhost
PERCH_DB_PREFIX: perch2_
PERCH_EMAIL_FROM: adam@bristlebird.com
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Zend: 3.0.0
OS: Linux
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GD: Yes
ImageMagick: No
PHP max upload size: 64M
PHP max form post size: 64M
PHP memory limit: 512M
Total max uploadable file size: 64M
Resource folder writeable: Yes
Session timeout: 24 minutes
Native JSON: Yes
Filter functions: Yes
Transliteration functions: No
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