Dear Olga,
meanwhile I found the solution! The footer block was not set on the “SHOP” website. After setting up that page all products appeared properly!
But another error came up. I translate the page into Hungarian with the Loco translate plugin. After the 6.3.3 update I had to translate the whole thing again, but this time I will rewrite the corresponding Hungarian translations in vain, they will not appear, they will remain in English.
If you could help me with that, I would thank you 🙂
Attila