Thumbnails not compressed

Dear Hueman support team,

Thank you for your awesome theme.

I am currently testing my website:
https://www.webpagetest.org/result/160416_H9_PJY/1/performance_optimization/#compress_images

It says that the following images are not compressed:
FAILED – (57.6 KB, compressed = 25.9 KB – savings of 31.7 KB) – https://blog.defi-ecologique.com/wp-content/uploads/Xavier-Boinet2-520×245.jpg
FAILED – (59.4 KB, compressed = 28.7 KB – savings of 30.7 KB) – https://blog.defi-ecologique.com/wp-content/uploads/featured_dd_internautes-520×245.jpg
FAILED – (56.2 KB, compressed = 26.1 KB – savings of 30.2 KB) – https://blog.defi-ecologique.com/wp-content/uploads/featured_dd_politique-520×245.jpg
FAILED – (51.4 KB, compressed = 23.2 KB – savings of 28.2 KB) – https://blog.defi-ecologique.com/wp-content/uploads/TobyHudson-520×245.jpg
WARNING – (68.6 KB, compressed = 43.9 KB – savings of 24.7 KB) – https://blog.defi-ecologique.com/wp-content/uploads/0geeketbio-520×245.jpg
WARNING – (68.4 KB, compressed = 56.8 KB – savings of 11.6 KB) – https://blog.defi-ecologique.com/wp-content/uploads/pub-defi-ecologique.jpg
FAILED – (21.5 KB, compressed = 10.4 KB – savings of 11.1 KB) – https://blog.defi-ecologique.com/wp-content/uploads/0geeketbio-160×160.jpg
WARNING – (30.5 KB, compressed = 21.2 KB – savings of 9.3 KB) – https://blog.defi-ecologique.com/wp-content/uploads/0sejourne-520×245.jpg
WARNING – (17.9 KB, compressed = 9.3 KB – savings of 8.6 KB) – https://blog.defi-ecologique.com/wp-content/uploads/featured_dd_politique-160×160.jpg
FAILED – (16.3 KB, compressed = 8.1 KB – savings of 8.2 KB) – https://blog.defi-ecologique.com/wp-content/uploads/Featured_rolet-160×160.jpg
WARNING – (15.1 KB, compressed = 8.2 KB – savings of 6.9 KB) – https://blog.defi-ecologique.com/wp-content/uploads/featured_dd_internautes-160×160.jpg
FAILED – (13.4 KB, compressed = 6.7 KB – savings of 6.7 KB) – https://blog.defi-ecologique.com/wp-content/uploads/0hancock-160×160.jpeg
WARNING – (13.4 KB, compressed = 7.1 KB – savings of 6.3 KB) – https://blog.defi-ecologique.com/wp-content/uploads/sandpuppy-160×160.jpg
WARNING – (13.7 KB, compressed = 7.4 KB – savings of 6.3 KB) – https://blog.defi-ecologique.com/wp-content/uploads/Tamaki-Sono-160×160.jpg
FAILED – (10.6 KB, compressed = 5.0 KB – savings of 5.6 KB) – https://blog.defi-ecologique.com/wp-content/uploads/Barn-Images-160×160.jpg
FAILED – (11.1 KB, compressed = 5.5 KB – savings of 5.6 KB) – https://blog.defi-ecologique.com/wp-content/uploads/0yann-160×160.jpg
WARNING – (11.2 KB, compressed = 6.4 KB – savings of 4.9 KB) – https://blog.defi-ecologique.com/wp-content/uploads/0sejourne-160×160.jpg
WARNING – (8.0 KB, compressed = 4.1 KB – savings of 3.9 KB) – https://blog.defi-ecologique.com/wp-content/uploads/herder3-160×160.jpg

Well, I have used Smush It and Compress JPEG & Tiny plug-ins, which both indicates that it is fine.

Since most of these images are non-standard thumbnails, I was wandering if you had any idea if that caused the “non-compression” of said images ?

Thank you for your help !

Regards