Call to undefined function mb_orig_strpos?

Question

PHP

When opcache is enabled, the following error occurs:
Call to undefined function mb_orig_strpos
and then the path to the file
. If it is disabled, there is no error, but the whole site slows down (I have not installed memcached yet).
I did not find such a function - I shoveled github and google in search.
Google has always returned similar code:

CTar::strpos()
//    /bitrix/modules/main/classes/general/backup.php:1410

    public static function strpos($s, $a)
    {
        if (function_exists('mb_orig_strpos'))
            return mb_orig_strpos($s, $a);
        return strpos($s, $a);
    }

Here, as you can see, the check for the existence of the function is in progress. Yes, and in other files too.
Simply disabling opcache (this is what technical support recommends) is not an option, I think.
Perhaps bitrich is completely incompatible with php7?
I will be grateful for your help :)

Answer 1

look towards php.ini
mbstring.func_overload = 2

Answer 2

1. look towards php.ini or .htaccess
mbstring.func_overload = 2
2. Disable the proactive filter
3. mbstring.func_overload = 0
4. update Bitrix