I'm using Threema as a messenger on my mobile phone.
When I enable SSL/TLS Inspection it is no longer possible to send or receive images through Threema.
Only if the feature is completely turned off, I'm able to send or receive images.
There are not defined rules for Decryption. Just the default setting.
I already tested it with v18 GA.
The issue is still there in v18 GA.
I would like to troubleshoot this issue with someone from Sophos.
As Threema is a paid app, it is hard for us to test in house.
I will PM you to do troubleshooting.