This occurred because you did not check whether the folder exists and another detail instead:
RewriteRule ^painel - [L]
Prefer this:
RewriteRule ^painel/ - [L]
Without the bar . htaccess will accept addresses as localhost/painel2 and supposing it is a route it will become inaccessible.
Getting back to the problem, you probably did something similar to this in your . htaccess: /a/91799/3635
First solution
Must be using similar to this:
/home
  |--- /user
         |--- /public_html
                |--- .htaccess (seu .htaccess)
                |--- /public
                        |--- index.php
                        |--- .htaccess
                |--- /app
                |--- /bootstrap
                |--- /config
                |--- /database
                |--- /painel (pasta do painel)
If you want the panel folder here to be accessible the public_html/.htaccess should look like this:
RewriteEngine On
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^ public/ [L]
Second solution
However the best thing is to stay inside public same, then the structure would be so of the folders being this (public_html is a common folder on servers, may have another name like www), see that I moved the location of the panel folder inside public:
/home
  |--- /user
         |--- /public_html
                |--- .htaccess (seu .htaccess)
                |--- /public
                        |--- /painel (pasta do painel)
                        |--- index.php
                        |--- .htaccess
                |--- /app
                |--- /bootstrap
                |--- /config
                |--- /database
So in this case the file public_html/.htaccess must contain:
RewriteEngine On
RewriteRule ^ public/ [L]
And the file public_html/public/.htaccess must contain:
<IfModule mod_rewrite.c>
    <IfModule mod_negotiation.c>
        Options -MultiViews
    </IfModule>
    RewriteEngine On
    # Redirect Trailing Slashes If Not A Folder...
    RewriteCond %{REQUEST_FILENAME} !-d
    RewriteRule ^(.*)/$ /$1 [L,R=301]
    # Handle Front Controller...
    RewriteCond %{REQUEST_FILENAME} !-d
    RewriteCond %{REQUEST_FILENAME} !-f
    RewriteRule ^ index.php [L]
</IfModule>
Third solution
But I have to say, you can even use . htaccess to point everything to public, however the best way is to define the DocumentRoot as being the public or release the content of public in public_html and the folders of the windows will be out, something like:
/home
   |--- /user
         |--- /app
         |--- /bootstrap
         |--- /config
         |--- /database
         |--- public_html (conteúdo de public deve ficar nesta pasta)
              |--- /painel (pasta do painel)
              |--- index.php
              |--- .htaccess