Re: Product not showing in specific category pages on frontend
If this issue if for only even/odd no or pages or you can find a pattern among them. I will suggest to check this as an issue of your module or any third party module. To dig this deeper you should disable all modules that have preferences related to catalog and plug-ins related to product entity.
Try disabling them one by one and make sure you reindex and flush cache to be double sure that your module is no longer in use, and narrow down your third party/custom module list.
There is no such issue in Magento core specially in 2.1.7 .