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:

ICMP host aaa.bbb.ccc.ddd unreachable - admin prohibited filter, length 68