Error on edit markdown

- Vim bootstrap version(number in first line): No version given
- Operating system: MacOS Catalina
- Vim/Nvim version: VIM - Vi IMproved 8.2 (2019 Dec 12, compiled Sep 21 2020 04:03:24)
- Languages: markdown

## Description

I writing a new Markdown file and when I add a new code block with the sequence of characters "```", the editor auto-remove the third "`" caracter. I tried to remove markdown as an available language on vim-polyglot and remove conceal thinking that it, but it not solve the problem.

The lines that I add to vimrc file was:
```set conceallevel=0
let g:vim_markdown_conceal = 0
let g:vim_markdown_conceal_code_blocks = 0
```
Please can you help me?