Opening and/or downloading StartMail's file attachments fail

When I use my StartMail email provider via the Aloha app on my iPhone SE 2022, Aloha does not let me open common file attachments for reading (e.g.: pdf, jpeg etc.). But instead, Aloha immediately offers to dowload the file, and when accepted to dowload it fails on every attempt, also via 'Open Source Page' showing a quick popup message: "Download error" and after that: "Download failed". In this case the big screenshot of two-in-one shows my StartMail inbox with an attached pdf file that Aloha didn't open nor downloaded. On the lower right corner the smaller screenshot shows two failed download attempts. The complete link/url from the portion shown at "Open Source Page" of the relevant pdf file is:

https://mail.startmail.com/api/Messages/INBOX.2867/Attachments/2

On the other hand, when I use StartMail via the Safari app on my iPhone, Safari has no problem to open (for reading) and/or to download these common file attachments, but works just fine with them. And when I use my Outlook email provider via the Aloha or Safari app on my iPhone, both Aloha and Safari have no problem to open (for reading) and/or to download these common file attachments, but work just fine with them. Apart from the two screenshots related to the problem, I've also made a seperate two-in-one screenshot of my Outlook inbox and Aloha's succeeded download of the same relevant pdf file attachment.

The problem seems as if the Aloha app has some sort of conflict with the StartMail email provider, when it comes down to handling the common file attachments. Hopefully Aloha's Support Team is able to figure it out that could help solving the problem.