Hi @xaashi20,
Thanks for contacting us.
We have checked this issue at our end but couldn’t replicate it. The post featured image is shown correctly according to the plugin’s setting.
Can you please check what width and height are defined for medium size images? Ideally they should be higher than thumbnail size. You can check it from WP Admin Dashboard menu Settings –> Media. We have attached a screenshot here for a reference.
If the above setting is correct, then we suspect the issue can be due to conflict with the active plugin or theme. In that case, we would recommend performing a conflict test on the site. You may need to temporarily disable all other plugins except the Email Subscribers plugin and switch to a default WordPress theme.
Also to ease the debugging process, you can install Health Check plugin which disables all the plugins and switches the current theme to the default theme only for the current logged-in user when troubleshooting mode is enabled. It does not affect other users or site visitors. You can get the Health Check plugin from here. After enabling the troubleshooting mode, activate the Email Subscribers plugin, and check if the issue is resolved or not.
Hope this helps you. Let us know what comes out. Also, let us know if you have any further queries.
Thank you.