Well i have the exact same problem, and each and every time i start or load a campaign game, i get a message telling me my internet is down, which it isn't.
Needless to say my copy of SH5 is legit, i bought it from gamesload.fr.
I tried re-installing, of course, but it wouldn't work, i then tried re-downloading the files using gamesload download manager and reinstall, with no better results.
I'm thinking maybe it could be a problem with windows registry or the serial key being used by another person? But then, how comes the ubi launcher connects fine in the first place?
I hope we can solve this problem quickly, because i'm actually beginning to enojy sh5, thanks to all the mods found here!
Salute!
Louis.
Here's a link to another thread about same issue:
http://www.subsim.com/radioroom/showthread.php?t=165373