Hello!
Have no idea why, but regardless to settings of your plugin (I tried both options – manual use and automatical for all WP pics, also tried different lightbox scripts) I see lightbox working only in the desktop Chrome browser, at Firefox, Safari and mobile Chrome and Safari it doesn’t work but just open the picture.
Link with an example – try to click to the thumbnails at the gallery (attention, NSFW content): https://allswingersclubs.org/swingers-club/club-amorous-420/