Backend 404 error after "Home" page update

NEED HELP URGENTLY !

This problem keep on happening everyday now and made me mad.

I keep on working on the home page these days.

Not every time, but it happened 2 out 3 page updates. Whenever I finished update the page and click the update button, the page refresh and return with 404 page not found error in the installed theme’s template. This happened in the backend, and the page concern is still intact and viewable in front end.

I thought there may be some plugins that is not compatible with the theme or the page composer. I then try to deactivate some plugin. After the deactivation, I try to open the same Home page in the backend and no more 404, i.e. page can be opened for edit and update again this time.

OK, after a few more back and forth edit and update, the same problem come again. I then tried to deactivate another plugin, then everything is back to normal again. And after a few more edit and update,the same 404 error come again and I tried again to deactivate another plugin and back to normal again……..this cycle of 404 and plugin deactivation seems never ended.

Now it comes to the worst situation. I have to deactivate all the plugin in order to do edit and update to my Home page. The activate all the plugin after the Home page updated is done.

Any opinion what caused this annoyance, or better name it disaster?

For information, I am running
PHP 5.3.28 (hostdime shared hosting)
WP 3.9.1
Theme: Jupiter 3.9.3 with page composer.
Site built with woocommerce and WPML

below are my .htaccess:

# These Lines Added By Hosting Company please do not remove
<IfModule mod_suphp.c>
suPHP_ConfigPath /home/lawlo/public_html/
</IfModule>

<Files php.ini>
order allow,deny
deny from all
</Files>
# End of Hosting Company Entries

# -FrontPage-

IndexIgnore .htaccess */.??* *~ *# */HEADER* */README* */_vti*

<Limit GET POST>
order deny,allow
deny from all
allow from all
</Limit>
<Limit PUT DELETE>
order deny,allow
deny from all
</Limit>
AuthName novawebsolution.com
AuthUserFile /home/lawlo/public_html/_vti_pvt/service.pwd
AuthGroupFile /home/lawlo/public_html/_vti_pvt/service.grp

# 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

Thanks for any opinion and advice.