Attachments not shown

Expected behavior

When you recieve an email that has an attachment it should be shown/available for you to download, regardless of sender.

Actual behavior

The attachments behaviour is not consistent, here's a thorough explanation of the situation:

-Most emails with attachments display correctly, however I've noticed that dmarc emails sent by google to our noreply email do not shown the attached zip file containing the report, yahoo's dmarc emails are showing attachments, but not gmail's.

Here's a screen shot showing the inbox in mail app:
https://i.imgur.com/igz3YgW.png
You can notice that only the 2nd email (which is yahoo's) shows an attachment, all gmail dmarc reports are showing without attachments.

Here's the same email inbox, but using roundcube instead of NC mail app:
https://i.imgur.com/7rtQSVW.png
As you can see every single email has an attachment if I use roundcube to explore the emails, but not NC's email app.

The behaviour is very confusing to me, I do not understand why would one email display an attachment but not the other.

Mail app

Mail app version: 1.8.0

Mailserver or service: EXIM/Dovecot

Server configuration

Operating system: Ubuntu 18.04

Web server: Apache

Database: MySQL 10.3.22

PHP version: 7.4.7

Nextcloud Version: 20.0.5

Client configuration

Browser: Firefox 84.0.2

Operating system: Windows 10

No source file or test is named. Start by reproducing the issue with Gmail and Yahoo DMARC messages, compare the Mail app with Roundcube, and trace how attachments are detected and presented. Done means the Gmail DMARC ZIP attachment is consistently shown and downloadable.