My wife has had a few messages "disappear" from WeChat (the Chinese Facebook), and that were not removed by group admins. It seems that at the low end, at least, they're content do just censor, and not take action against the speaker.
Is she in China or overseas? WeChat has different censorship policies for domestic vs foreign accounts, and silent blocking sometimes occurs when foreign accounts communicate with domestic accounts about sensitive topics [1]. It's also not encrypted, and it appears messages are automatically getting forwarded to the local (Chinese) police for investigation [2].
[1] We (can’t) Chat “709 Crackdown” Discussions Blocked on Weibo and WeChat: https://citizenlab.ca/2017/04/we-cant-chat-709-crackdown-dis...
[2] Over 300 million Chinese private messages were left exposed online: https://www.theverge.com/2019/3/4/18250474/chinese-messages-...
Fair enough. This was with an account that was registered within China, but the traffic is physically originating from the USA.