For Wordpress website used Rich-Snippet Plugin, that added schema for pages using Microdata. I also applied Sitelink Search Box, Product schema, Article Schema For the Same site in different pages using JSON-LD language. is it conflict or not? or Harmful for any site. I want know the actual reason behind it. Please let me know?
Gary said by using JSON-LD and Microdata on same page does not create any problem.
Google search console will display both markup, but Google may be merge it or will prefer JSON-LD markup over microdata if it is available.
If you do not have microdata and json-ld on the same pages, you will not have an issue.
If you have it on the same page, according to this quora post, you will not have an issue if the microdata and json-ld are referencing different entities you will not have an issue.
The problem will be when you are referencing the same entity with the microdata and the json-ld data. When the two referencing the same entity, google or other search engines could mis-interpret the information on the page.
I think that you can mark up different things in different vocabularies/syntaxes with no issue. But you can cause conflict if you mark up the same thing multiple times. Google will typically pick one and ignore the others.
Another issue is that systems like Google need to determine what markup represents the pages content. If you separately mark up the page as an Article as well as a Product, then you are sending conflicting signals on what the page is about.
Best practice: a single entity can be multiple types