Have you enabled Cloudflare on the site? This can cause issues.
If the issue isn’t related to Cloudflare, the first step to debug the issue is to try using your forum in safe mode. If the problem still happens in safe mode, the next step is to remove any non-official plugins from your site’s
app.yml file and rebuild the site with
./launcher rebuild app. If this doesn’t solve the issue then we’ll need to look at what’s going on.
Before removing plugins, you might want to visit your site with your web inspector open to its console tab. Try creating a post and look for any errors reported in the console. You could also go to your site’s logs at Admin / Logs / Error Logs and look for any errors that are reported in the logs. This may help to point out what is causing the issue.