temporarily disable firewall completely?

post your ss2tool.log and try to wait for @Kolya but linux users are pretty much on their own. //ignore that last bit, this is win7 x64.

shoot I was looking at the linux topic right before posting that. technically still true though.

anyway, things that can be tried in the meantime:
-hardwire to the router
-use the phone as hotspot
-try a different (win10?) pc

@maxdamage: You don't need to install rsync. It gets temporarily installed by SS2Tool. As soon as it tries to make a connection you should generally see a windows firewall pop up which you simply allow. If that doesn't happen, there's a few things you can try (check after each of these if SS2Tool works):
- make sure that you placed SS2Tool inside your game folder
- check your firewall rules and remove any that apply to rsync
- rename the game folder
- post your SS2Tool.log here

@maxdamage: You don't need to install rsync. It gets temporarily installed by SS2Tool. As soon as it tries to make a connection you should generally see a windows firewall pop up which you simply allow. If that doesn't happen, there's a few things you can try (check after each of these if SS2Tool works):
- make sure that you placed SS2Tool inside your game folder
- check your firewall rules and remove any that apply to rsync
- rename the game folder
- post your SS2Tool.log here

Unfortunately no log is left in the root of the game folder after I close the app, not even when I rename the game folder.

Get a notification from my anti-virus Avast it has blocked access to https://www.systemshock.org/ because one of the issuers of the server certificate has expired when the app tries to send a log to this site.

Doubt that could be the cause though?

The site has a valid server certificate as you can easily look up in your browser right now by clicking the lock symbol next to the URL.
Which mods are you referring to that get flagged by your antivirus? And what is your antivirus?