On 2021-12-01, there was blocking by TSPU of WebRTC (specifically DTLS) with a certain fingerprint: OONI reports of Tor blocking in certain ISPs since 2021-12-01 - #3 by ValdikSS. This blocking was evidently targeted at Snowflake. After fixing the DTLS fingerprint (Make Snowflake's DTLS fingerprint more similar to popular WebRTC implementations (#40014) · Issues · The Tor Project / Anti-censorship / Pluggable Transports / Snowflake · GitLab), Snowflake began working again, and it has worked since.
One possibly important difference is that Snowflake does not use TURN servers. Unlike a chat application, the Snowflake client does not care which proxy it has a WebRTC connection with, so a central server matches clients with proxies according to NAT type so that a TURN server is not needed.