Code disappear sometimes from .htaccess - wordpress

Question

Hello guys i’m new and I have question. I have one website that have indexed https and http version in google search, and I added 301 redirect from HTTPS to HTTP in .htaccess. Sometimes, Randomly, 301 redirect disappeared from htaccess and I need to add it again.
This is my htaccess with 301 redirect:
# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteCond %{HTTPS} on
RewriteRule (.*) http://%{HTTP_HOST}%{REQUEST_URI} [L,R=301]
RewriteBase /
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>
# END WordPress
And After some times, they change to this
# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>
# END WordPress
So the redirect was completely removed, google index again https page and I need to add it again, why? I tried many hosting company but nothing changed.

Answer 1

I would not redirect vom HTTPS to HTTP, but the other way round. Google will give you a small ranking boost if you are using HTTPS (not to speak of it being the right thing to do to protect your users' privacy).
That being said: don't put anything between the WordPress markers, e.g.
# BEGIN WordPress
....
# END WordPress
WordPress will overwrite it the next time it writes to the .htaccess.
If you put it before that block, i.e.
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteCond %{HTTPS} on
RewriteRule (.*) http://%{HTTP_HOST}%{REQUEST_URI} [L,R=301]
</IfModule>
# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>
# END WordPress
You should be fine, and it should remain intact.

Answer 2

Thanks #janh, so this is correct?
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteCond %{HTTPS} on
RewriteRule (.*) http://%{HTTP_HOST}%{REQUEST_URI} [L,R=301]
RewriteBase /
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>
# BEGIN WordPress
# END WordPress