I did not have this problem for a long time and in last 2 weeks 3 instances.
PayPal payment is coming, but "0" orders under customer info in Admin.
I have to e-mail customers to ask what did they order.
I did not change anything on Zen Cart part.

It looks like a random event.

How to check that IPN is on in Paypal?

Any suggestions are appreciated.

We know, we behind in update, but can this be the main issue, system works in 95%?

Thank you for your time in advance.