There is a post from 2014 that seems similar.
MacBook Air (M1, 2020), 16GB RAM, macOS Big Sur, Version 11.2.3 (20D91)
Microsoft Outlook, Version 16.46 (21021202), Microsoft 365 subscription
Tested on both EagleFiler 1.9.3 and 1.9.4b1
With an EagleFiler library open, I select a message in Outlook and press Fn-F1. There is an approximately 2 min delay during which EagleFiler does not respond. When the process times-out, a message is displayed in Outlook (attached image), “Error exporting message” with three options 1) Just Import Headers, 2) Skip All Empty Messages, and 3) Cancel.
I tried moving the message to a folder “On My Mac” in case the message wasn’t fully downloading but saw the same issue.
If I drag and drop the same message to the Finder, it is blank except for the header.
Interestingly, I am able to import messages successfully using the default “Import From Outlook” AppleScript.
Additional info: I created this EagleFiler library on an Intel based MacBook Pro (macOS Big Sur, Version 11.2.3) earlier in the day and imported approximately 4000 messages from Outlook 2016 (16.16.27) using Fn-F1 with no problems.
Any suggestions would be appreciated. Thanks