Firewalls won't cause the game from opening like this, nor will restarting a router. Any networking issues won't cause a crash on startup.
Let's try two options here:
Try installing FeralHeart into a new folder on your computer so that no old FeralHeart files will cause an conflicts with this new version. To do this:
Download that, run it and when it comes to this:
PICTURE LINKType a 1 in the box so it looks like this:
PICTURE LINKIf that doesn't work:
If you have an anti-virus installed try disabling it, deleting the FeralHeart folder then reinstall and try to get it run. Your anti-virus could be eating some files that the game needs to run properly. So even though you uninstalled and reinstalled, it won't make a difference since it will continue to remove those files. If doing that fixes your issue then you're going to have to set up your anti-virus to not scan the FeralHeart folder anymore.
Sorry that was vague but every anti-virus is different in how they're set up so I can't go into detail.