Pictures on front page gallery broken – Limon Theme

I have recently updated a friend’s website to use the Limon Theme by Two2Twelve and I am having trouble with the image gallery on the main page. The pictures should sit in the relevant boxes and automatically generate a thumbnail so it looks neat. Then when the visitor clicks on the image it will display a full sized version but it’s not working. The Images are not generating thumbnails and instead are displaying the corner of the image as they won’t resize.

Here is the website: https://doan.dk/

The problem is on the front page just below the slider.

I have used this theme before and had no problems at all with the front page gallery. I have contacted Two2Twelve but they have not replied yet. I have tried disabling all plugins except qtranslate as that caused an error. Although I have used qtranslate and this theme together before without problems.