Hi!
1. Can you please share a link to a page where the plugin is active? If the items do not appear only some of the time, that means it more likely a cache related issue. Make sure to clear all layers of site cache, including minify, CDN page etc..
2. I can check, but it very highly depends on the borwser. Some browsers can handle these previous states, but some of them may not. Usually IOS/Mac browsers are the worst of all, especially Safari, it has it’s own way to handle prev/next states, which can not be controlled.