If you put the CMS in debugging mode and then force the feed to parse (edit&save should do it or create new widget with the feed), then if you look at Logs page, are there any errors?
If there are errors, are there still about certificate or something else?
Thanks for your fast reply.
My CMS version is 1.7.8.
I enabled the debugging mode and recognized a line in the log which says :
“120791 17-09-18 01:11:05 CMS module Feed Error: cURL error 60: SSL certificate problem: self signed certificate in certificate chain”