I digged a bit and found this in VirtueMartModelProduct
//This option switches between showing products without the selected language or only products with language.
if( $app->isSite() ){ //and !VmConfig::get('prodOnlyWLang',false)){
if((empty($this->keyword) or $group !== FALSE) and self::$omitLoaded and self::$_alreadyLoadedIds){
$where[] = ' p.`virtuemart_product_id`!='.implode(' AND p.`virtuemart_product_id`!=',self::$_alreadyLoadedIds).' ';
//$where[] = ' p.`virtuemart_product_id` NOT IN ('.implode(',',self::$_alreadyLoadedIds).') ';
}
} else {
//$joinLang = true;
}
When I removed this code part, the server worked fine.
As far as I can see, it's mod_virtuemart_products. I disabled 'omitLoaded' in every module, I don't need it actually, but maybe it worth to check. I'm not sure WHY the 'NOT IN' version was replaced to this