Empty RSS mail

Empty RSS mail

Hello,
I have sometimes my RSS feeds sent without items, empty content sent !
In the FAQ, i can see that :

2. What if there's no update or new content in the website or blog. Will it trigger the RSS Campaign?
In this case, no campaign would be sent.
see  https://www.zoho.com/campaigns/help/advanced/rss-faqs.html

What could be wrong ? Why Zoho Campaign send empty emails ?
Perhaps a not empty RSS feeds that contains wrong characters ?

How can i debug that ?
Thanks in advance