Unable to connect to GCE instance via ssh after removing 0.0.0.0/0 rule from the FW
Quick way to debug the problem try ssh from the CLI , from an authorized IP, if you are getting response like the below, then the FW rule is working.
Koreshs-iMac-2:~ omid$ ssh 18.104.22.168 The authenticity of host '22.214.171.124 (126.96.36.199)' can't be established. ECDSA key fingerprint is SHA256:FIhYUjgJp+b+F7zuadEg4h7UXWSAzdYpyHVsu8OUg8A. Are you sure you want to continue connecting (yes/no)?
If not – then you have several other reasons for these to fail. 
If you are trying to connect via SSH using the GCE console gui and it is not working then you are not using your IP, in this case you are getting a dynamic IP on Google IP ranges and the firewall rule haven’t these sources. On
good step by step manual get the public IP ranges of google :
based on this blog:
nslookup -q=TXT _netblocks.google.com 188.8.131.52 nslookup -q=TXT _netblocks2.google.com 184.108.40.206 nslookup -q=TXT _netblocks3.google.com 220.127.116.11
and then based on the results of each command run something like:
nslookup -q=TXT _netblocks.google.com 18.104.22.168 Server: 22.214.171.124 Address: 126.96.36.199#53 Non-authoritative answer: _netblocks.google.com text = "v=spf1 ip4:188.8.131.52/24 ip4:184.108.40.206/19 ip4:220.127.116.11/20 ip4:18.104.22.168/20 ip4:22.214.171.124/18 ip4:126.96.36.199/16 ip4:188.8.131.52/21 ip4:184.108.40.206/16 ip4:220.127.116.11/17 ip4:18.104.22.168/19 ip4:22.214.171.124/19 ~all"
how can connect via ssh from my ip on the terminal? instead of using the gui
Using your terminal, in this document you find information about how to do this  . With first document you provide and configure the public key and in the second document you find an explanation about how to connect using SSH command.
I put a lot of thoughts into these blogs, so I could share the information in a clear and useful way. If you have any comments, thoughts, questions, or you need someone to consult with, feel free to contact me:
Contact me at-