I used to use version 5.600 for years, quite content and now I have reverted to it. Because files atteched to a mail aren’t sent at all.
Here’s the case. I use Crewnerd, an app for collecting data during a row outing. Once finished with training a ca recall the training from the history and even send TCX, KML or GPX files by mail. This is all handled by Android. I sent the mail from 5.600 and the attachement is delivered. Sending from 5.8xx will not attach the file.
Make sure that the app still has permission to access storage. Maybe something happened during the update that disabled it
K-9 no longer uses the storage permission (starting with new Android versions, the permission can only be granted to file manager apps that need to manually get the permission by Google). In modern apps, the app that shares the attachment is responsible for giving permissions to K-9 (using a content uri). Apparently, the app you are sharing from only provides a plain file path without granting K-9 the permission to use the file.