Did your instances have external IPs? We had connectivity issues when using NAT due to it dropping SYN packets. We just gave everything that needed to talk to external IPs their own external IPs.
Glad you found a workaround, but please file a support ticket for this. If you don’t have support: (a) consider it and/or (b) send me an email with your info (contact in profile) and I’ll file a bug.
We actually did have a dedicated Googler who oversaw our move from AWS to GCP. I asked him about it but never got a reply.
Anyway, yes. It caused us problems. Attempts to connect to machines outside of GCP would fail repeatedly due to the NA dropping the SYN. This would mean our connect() call would timeout repeatedly. There was an ICMP response I could see with tcpdump:
