Some major .htaccess help

Hello,

This website I am working on had a messed up .htaccess about two months ago, which is supposed to be fixed, but the googlebot keeps on finding lots of 404s, there is over 40,000 of them in webmaster tools. These pages are not in the google index, or sitemap, nor any links from any other pages, as far as we can tell. It seems to be some error in the .htaccess file.
google is not crawling pages anymore like it used to, pages are being dropped out of google index, traffic has gone down. So I would really like to get it fixed as soon as possible.

This is part of the file:

#Options +FollowSymLinks

php_value error_reporting 1

<IfModule mod_rewrite.c>
	RewriteEngine On
	
	RewriteCond %{HTTPS} !on
	RewriteCond %{HTTP_HOST} ^website.com [NC] 
	RewriteRule ^(.*)$ http://www.website.com/$1 [L,R=301] 
	
	RewriteCond %{HTTPS} on
	RewriteCond %{HTTP_HOST} ^website.com [NC] 
	RewriteRule ^(.*)$ https://www.website.com/$1 [L,R=301] 
	
	RewriteRule ^(.*)\/function\.mkdir$ /$1 [L,R=301]
	
	RewriteRule ^google2a182b0273bc.html$ - [L]
	RewriteRule ^google493735a2a7cd7.html$ - [L]
	
	RewriteRule (.*)\.html$ $1.php [L]
	RewriteRule (.*)sitemap\.xml$ sitemap_area.php [L]
	
	RewriteRule api - [L]
	
	RewriteRule ^(.*)\/$ /$1 [R=301,L]
	
	RewriteCond %{REQUEST_FILENAME} !-f
	RewriteCond %{REQUEST_FILENAME} !-d
	RewriteRule . frontend/index.php [L]
	
	RewriteCond %{REQUEST_URI} !^/robots.txt
	RewriteRule ^[A-Z]{2}-.* /php/profile.php [L]
</IfModule> 

#RedirectMatch 301 ^/(.*)\/$ /$1

Code (markup):

If you can help me, please let me know.

 

What web application are you running? What URLs are being 404'd?

 

It was a custom cms. There was all kinds of urls being 404ed.

It was way over my head, so I got some outside help.

Thanks anyways.