All products are sold out

We wanted to switch our live system to WebPOS today and now we have a big problem: All products are sold out, even though WooCommerce has them in stock!
This is a big problem because we can’t use WebPOS.
What could be the reason for this? How can we fix it?
I can’t share the WP admin login details because it’s a live system where we don’t allow testing.
The staging site does not have this problem.

I need a quick solution on this!