Need an expert in PHP coding.

I have a WordPress plugin that is no longer supported but works just fine except for one thing that recently broke with either a WP upgrade or my addition of SSL to the website. Probably the former. It's probably just a single line of code that needs to be fixed, and I have some tips where to look from the developer that would make sense to someone who speaks PHP. I also have screenshots of how the error manifests itself.

Also, I'd like a copy of the code with annotation about what was changed, just in case this happens again.

I really want to keep this plugin, and the plugin developer "no longer does WP", so I'm asking here on PPH. Thanks.