Thumbnail image issue

Please identify exactly which theme you are using and then post in that theme’s dedicated forum via its page in the Theme Repository so the theme’s developers and support community can help you with this.

Sure, but I could find iPress in that link you supplied.

iPress is a commercial theme. For commercial product support please contact the author directly on their site.

https://themeforest.net/item/-ipress-blogmagzinenews-wordpress-theme/10053609

Forum volunteers are not given access to commercial products, so they would not know why it is not working properly. Keep in mind we encourage you to use the official support venues, as it allows the developers to be aware of issues with their code and gives back to the community in a more robust way. See https://www.ads-software.com/support/guidelines/#do-not-post-about-commercial-products

check the iPress documentation for image size. or try to change the size on the main wp settings to test if is working