Thumbnails not showing on index / archive pages

Hi there,

I was running the free Neutica theme and was having a problem with the thumbnails. If I tried to add an image from the media library to a post, the image would not appear as a thumbnail on the archive and index pages at all. I resolved this by uploading a new image for each post. I liked the theme so I upgraded to the paid version (the 2.0.06) but now the thumbnails won’t appear at all, even if I upload an image per post. They also do not appear on the fancy sticky post slider that’s touted as part of this paid theme. There is a plugin they suggest on their site to regenerate old images to fit, so I downloaded and ran that. Nothing. I already asked on their forums and also emailed them, but I’m beginning to get a sneaking suspicion that they might be a bit crap at support, as their forums only have answers from a few months ago. If anyone else has any idea about why this is happening (some sort of plugin conflict?) I would be most grateful.

My site is at https://www.diytelavivguide.com/blog

The theme lives here: https://themesupply.co/themes/neutica/

Thanks!