Hello, as one of your backers I'd like to congratulate you on an awesome game, apart from the rocky start you guys really pulled through. As for the problem it's my second copy of your game on GOG.
When starting a custom campaign bundled with the game, the game itself unpacks all the content in the "War For The Overworld\GameData\Maps\Saves" folder which using only one extra campaign inflates the folder size from 40mb to 200mb which in turn breaks the Galaxy Client's sync feature with syncing taking forever and in the end failing.
Unpacking all the custom campaigns goes up to 560mb with Galaxy when failing to sync alerts that the save games exceed the 400mb cloud space allocated to it.
The worst part is that while trying to sync the Galaxy app hogs so much bandwidth that every program requiring internet access fails - Steam loses connection to servers, you can't even open an web page, even the Galaxy client itself loses connectivity during the sync process. To make matters worse all devices on my local network have connectivity issues while GOG Galaxy tries and constantly fails to sync.
I'm guessing the problem appears because the custom campaign data gets unpacked in the saves folder where the Galaxy client is unable to differentiate real save game data and the content from custom campaigns.
Not sure why it uses so much bandwidth making my home network unusable, maybe because it tries to upload/download 200-560mb of data every time.
Current solution would be to not use sync or the Galaxy client, but it would be nice to have your saves backed up and being able to play community content.
Steps to reproduce:
Unpack the custom campaigns in the designated folder "War For The Overworld\GameData\Maps", go into the game and select Custom Campaigns which will unpack all the data to your "War For The Overworld\GameData\Maps\Saves" folder, then exit the game and watch as the Galaxy client struggles to Sync.
I have issued the same ticket to the GOG Galaxy staff as I think the problem could be solved by both sides, either separate the real save game data and the user made content or to better define which files the client needs to upload.
Thanks for your help.
Customer support service by UserEcho