Cache custom feed

I use some custom feeds (/feed/whatever/) that seems to not be cached but I had no problem with the default feed (/feed/).

This is the debug output for CUSTOM FEED:
</rss>
<!–
Performance optimized by W3 Total Cache. Learn more: https://www.w3-edge.com/products/

Page Caching using disk: enhanced{w3tc_pagecache_reject_reason}

Page cache debug info:
Engine: disk: enhanced
Cache key:
Creation Time: 1534481773.000s
Header info:
Expires: Wed, 11 Jan 1984 05:00:00 GMT
Cache-Control: no-cache, must-revalidate, max-age=0
Last-Modified: Thu, 16 Aug 2018 21:30:25 GMT
ETag: “88fc488442d85427ff9f31227b664fc7″
X-Powered-By: W3 Total Cache/0.9.7
X-Robots-Tag: noindex, follow
Link: <https://www.xiaomitoday.it/wp-json/&gt;; rel=”https://api.w.org/&#8221;
Content-Type: application/xml; charset=utf-8

Served from: https://www.xiaomitoday.it @ 2018-08-17 06:56:13 by W3 Total Cache
–>

This is the debug output for DEFAULT FEED:
<!–
Performance optimized by W3 Total Cache. Learn more: https://www.w3-edge.com/products/

Page Caching using disk: enhanced

Page cache debug info:
Engine: disk: enhanced
Cache key: https://www.xiaomitoday.it/feed/_index_ssl.html
Creation Time: 1534481918.000s
Header info:
Last-Modified: Thu, 16 Aug 2018 21:30:25 GMT
ETag: “88fc488442d85427ff9f31227b664fc7″
X-Powered-By: W3 Total Cache/0.9.7
X-Robots-Tag: noindex, follow
Link: <https://www.xiaomitoday.it/wp-json/&gt;; rel=”https://api.w.org/&#8221;
Content-Type: application/rss+xml; charset=UTF-8

Served from: https://www.xiaomitoday.it @ 2018-08-17 06:58:38 by W3 Total Cache
–>

What’s the problem?

Thank you