I have no idea why this particular image and others seem to be affected, but it's really annoying.
I have noticed, there is one image in particular that Wordpress just will not generate different images for.
I tested another image, and different sizes were created just fine. Went back to the original image, and even renamed it before uploading again, but still only the full size is uploaded and stored in the uploads
folder.
As other images seem to work fine, I don't think it's a server misconfiguration. But I'm stuck as to what I can do to try and diagnose.
The image itself is a JPG, and has only words and hypens in the filename
http://development.bellavou.co.uk/wp-content/uploads/lisa-wakeman-clinic-manager.jpg
UPDATE:
As pointed out, I hadn't given any information on the image sizes, but the image being uploaded is way higher than any of the settings below. Is there anywhere to find more information on when images are uploaded? Does Wordpress have it's own logging section?
Full size image: 4752 × 3168
WP Thumbnail: 150 | 150 (crop)
WP Medium: 360 | 360
WP Large: 1280 | 1280
FURTHER UPDATE:
After looking at the error logs, I see this message: development.bellavou.co.uk [Tue Feb 07 11:59:00 2017] [error] [client 81.137.229.53:47529] AH01215: Insufficient memory (case 4): /home/sites/bellavou.co.uk/public_html/development/wp-admin/async-upload.php
But Googling this 'Insufficient memory' doesn't yield many results. Does anyone know what could be needed here? Any why it only affects some images?
php -m
to see the modules that you have installed for PHP. If Imagemagick or Imagick is installed, then it is preferred over GD and you can try to manually downsize the image. If not, then GD is in use and you want to consider installing the Imagick extension for PHP (ask your hoster or on Serverfault). If that fails as well, then you will have to upgrade RAM on your server. Please edit the question with further progress.