So sorry to hear that you're having issues. We were aware of some multiplayer issues that came up with the recent update and just put out a hot fix the other day for it. Make sure your game is updated! I will be passing this issue along to the team to let them know that stuff is still a bit wonky.
If your game is updated to the newest version and you are still having issues with multiplayer, the option to revert to 1.96 is still available. I've copied and pasted the instructions on how to do that here for your convenience:
For those who are having trouble getting v1.97 to run; or who are hitting multiplayer issues, we have put up v1.96 on the opt-in beta branch, along with a 1.96 server.
To switch to v1.96:
1) Select Sins of a Solar Empire: Rebellion in your Steam Library
2) Click the Gear icon in the upper-right corner, select Properties
3) Click the Betas tab and select opt-in from the drop-down.
4) Steam will update you back to the 1.96 files.
If you wish to play online w/1.96, you need to manually update your settings file to point to port 7000.
1) Open Explorer to Documents\My Games\Ironclad Games\Sins of a Solar Empire Rebellion\Setting
2) Using Notepad, open rebellion.user.setting
3) Change line 42 to: IcoServerPort 7000
4) Save and exit the file
We are actively investigating why 1.97 has become so unstable and will post more when we figure things out. Our apologies for the hassle!