Ok I had similar happen a day or so ago, sans error message.
I eventually had to discarded the post entirely and start again. That worked. No need to log out from NodeBB (1.16.2), this was on Safari iOS 14.3 on iPhone.
I just activated the local emailer and getting a proxy error in /admin. Is this a bug? Hosting thru apache btw.
What do you see when you access your site without the proxy?
@julian I just disabled the local emailer and currently using mandrill but it doesnt send emails. The forum's not working as it should on some plugins..... gonna try reinstall