It's hard to say without seeing the site, the error logs, etc - they could be not showing up due to a php error where the host has upgraded php beyond what a ~12 year old install can support for example. Or the module might have a filter, I haven't used Products in a long time so not sure.
You might still be able to get the products exported though, essentially you'd need to create a template in the Products module that creates a csv. This tutorial is for Company Directory but can be adapted to other modules:
https://cmscanbesimple.org/blog/migrati ... ry-to-lise (skip the part about importing to LISE, just use it for learning how to make the csv).