Please note that the address for support is the official forum below:
https://www.patreondevelopers.com/c/patreon-wordpress-plugin-support/11
For that case you have, its likely that the post is not uploaded to/saved as an attachmet in WP in Media library. PW requires the image to be locked to be present in media library and needs it to have an attachment id.
From checking page code, no attachment info seems to be added to the inserted image on the page and it may not be present in media library.
You can try uploading it to media library, ensuring that it is there, and then inserting it via WP toolbar or other means into the post, and then locking it.