You found the issue! The master category id is invalid. I don't know why? Actually I didn't know about the Multiple Category Link Manager. I changed that and the product is showing up.
Now, how can I solve the problem for all the products. Shall I change all products manually? Or is there a way to change that setting in some other ways? When I click under product master category, I get only one option. Should I reset the master category ids from tools->store manager?
Thanks
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