categories not showing/saving…please help…don’t know coding

On my blog index and for each blog post, the breadcrumbs show “uncategorized.”
When I edit the blog post and add it to a category and then save it, the checkbox goes unchecked.
The blog post also does not take the blog category picture (plugin).
But the blog post does stay inside the category according to the collapsing categories sidebar widget.

I don’t know a lot of coding or anything, so I need serious help.
Thanks.