@miyukisaegusa You need to set the featured image for every gallery post. Did you do that? The recommended size is 474 * 342px. So, when you set the featured image size of 600*460px then automatically the 474*342px size image will be created so Image size should not be the issue. If you are still facing the issue, then you can send us your temporary username and password via https://www.themehorse.com/contact-us/free-support/ ( NOT HERE ) and I will look into it.
Thank you for your advice, I understood what “feature image” is! Now Gallery is working!
I have one more question.
I have two Gallery categories,
when I click the name of galley on my site , all images are gone and nothing shown.
How do I sort of them?
Seems like your caching plugin is caching the pages. When I tried to add new category and a gallery image, it didn’t showed up in the gallery page so seems liking caching issue to me