Permalink does not contain https and this causes HTTP Error 301 on all feeds

[peprdotcom]

We could not get Bloglovin to work with the feed ​https://www.agreencoconut.nl/feed. It turned out that while the whole blog was using https and also in the settings, content inside the feed wasn't . We found this by checking the feed validity:
​http://validator.w3.org/feed/check.cgi?url=https%3A%2F%2Fwww.agreencoconut.nl%2Ffeed%2F
Result: Server returned HTTP Error 301: The HTTP server returned a redirect error that would lead to an infinite loop. The last 30x error message was: Moved Permanently

When looking at the feed we immediately found that all links where not using https:

<channel>
	<title>A Green Coconut</title>
	<atom:link href="http://www.agreencoconut.nl/feed" rel="self" type="application/rss+xml" />
	<link>https://www.agreencoconut.nl</link>
	<description>Pura Vida</description>
	<lastBuildDate>Sat, 23 Jul 2016 01:22:50 +0000</lastBuildDate>
	<language>nl</language>
	<sy:updatePeriod>hourly</sy:updatePeriod>
	<sy:updateFrequency>1</sy:updateFrequency>
	<generator>https://wordpress.org/?v=4.5.3</generator>
	<item>
		<title>Nooit meer haast</title>
		<link>http://www.agreencoconut.nl/reizen/nooit-meer-haast</link>
		<comments>http://www.agreencoconut.nl/reizen/nooit-meer-haast#respond</comments>

WordPress-adres (URL): ​https://www.agreencoconut.nl/wp2
Siteadres (URL): ​https://www.agreencoconut.nl

We tried to fix this with "WordPress HTTPS" plug-in but no results.

It turns out that several parts of the feed contain errors. The atom:link, item link, guid link.

What can we do to fix this? It appears that some parts work but most don't. Help is appreciated.

[stevenkword]

I'm having trouble replicating this for the atom:link and item link elements.

​https://ma.tt/feed/

I am seeing this for the GUID, but technically, this doesn't require the protocol at all to be valid.

[stevenkword]

I'm closing this as "invalid" since I am not able to replicate the problem. The original reporter's feed also is not showing the reported problem currently, indicating that the problem might have been site-specific and has since been resolved.