If you're noticing you are not able to view or download attachments on the MacOS App, it may be the result of something going wrong in your logs.
To find your Polymail logs, we'd recommend you follow these steps:
Close the Polymail app
Open the Finder.app
Using the shortcut CMD + Shift + G
Type in ~/Library/Logs/Polymail Support.
It doesn't effect any other application or any files related to your macOS.