There is a bug on Webkul Marketplace extension I found,
Let I have two Marchant on the site and all the product assigns on one Marchant, so then when I go to product assign all vendor show empty product, but all product assign to one category.
On that file :
on product collection,
_prepareCollection (on this method)
->addFieldToFilter(‘entity_id’, [‘nin’ => $allOtherSellerProductIds]);
this line creates the problem. Because here empty value not check.
The whole first part should be
$collection = $this->_productFactory->create()->getCollection()
$collection->addFieldToFilter(‘entity_id’, [‘nin’ => $allOtherSellerProductIds]);
Note: If this is a bug and solved by me then please give bug bounty. Thanks.