.htaccess file keeps changing by itself

Good afternoon, I am unable to identify this problem. I have an SSL certificate installed by my host and works normally, so I put the following code in the .htaccess file:

RewriteCond% {HTTPS} off
RewriteRule https (. *): //% {HTTP_HOST}% {REQUEST_URI}

It works and redirects all my site to https. But the file changes alone quite often and remove this code, leaving the default WordPress .htaccess. I do not know if it could be a plugin or something else, I have the iThemes Security installed and it has access to .htaccess but I disabled and the problem remained, I do not know where to check, does anyone have any idea or have seen it?

Thank you in advance!

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