Issue with RSS/XML URL

Hello,

I have more and more issue with the validation of RSS url.
feeds are valid ( check on https://validator.w3.org/feed/check.cgi)
but reported with errors (505 or 403 or 503)
please find example here:
https://www.zataz.com/feed/

How can i solve that issue?

here other example
https://www.dealabs.com/rss/tout
https://www.planete-domotique.com/blog/feed/