Error when trying to edit slider

What a strange and roundabout way to create sliders… not even sure if the previous web guy did it correctly. Yes, the slider is presently working.

– Child theme for HitMag is implemented.
– Home (Front Page) is “Magazine Homepage” Template.
– Under Appearance > Customize > Slider Settings, the “Featured Slider” is ON and “-Show All Posts-” selected.
– Under “select slider” when editing this page, only shows “Home Slider”, no matter how many other sliders exist.

Now when I go to Appearance > Sliders, it does not matter how many sliders I create, only the one called “Home Slider” shows up in the select menu when editing the Home page.

Also under Appearance > Sliders, when I try to edit this slider, I get this very cryptic and poorly written error message:

This slider was created correctly, but the code implementation was delete from source code or blocked from filter.Delete this post or recovery slider implementation

So what would happen if I deleted this slider as instructed by the error message? It seems doubtful I’d be able to recreate it, since no other sliders that I create are showing up as select options on the Home page edit screen. So how to I clear this error message?