Hey there, everyone - thanks very much for waiting.
Our investigations on this one are ongoing, and our devs have asked me if anyone facing this issue can send over their save file? You'll find your save file here: %userprofile%\Documents\Anno 1800\accounts
Please zip up your save file, upload it to a third party file hosting service of your choice, and then send me a link to it here on this forum thread.
Once I've got your save file, I'll get it sent across to help with our investigation. Thanks so much in advance for the help, folks!