Question Submit button not working properly

I've installed Kunena on another website on the same new host and the problem doesn't arise there. It has the same version of Advanced Modules Manager (7.12.4). I downloaded the file from both websites and they're identical.

It can be many things which cause any errors. But a conflict can only occur with a module which running on the forum page. Maybe it's only a single module or the content of a module.
I've installed this module manager now (7.12.4), but also can't reproduce this problem (on my test page running PHP 7.3.17).
Try to disable the modules on the forum pages one by one). Disable also the top and jtouch-nav menu if there running over modules.

I've fixed it (I think!) by disabling the frontend module editing both in Advanced Modules Manager and in Global Configuration. They both control whether or not an edit icon appears when you float the cursor over the top RH corner of a module. Perhaps just enabling one or the other would have worked - I'll try that another day. That explains why there were two JS files with the same name - frontediting.js.

It doesn't explain why the issue only arises on the new host's server and not on the old host - it must be something to do with the server settings. Perhaps I should let Peter at Regular Labs know that there's a potential issue that he might be able to fix.

Thanks to you, I've learned something - which is how to use another bit of the developer tools on Firefox. It's a long learning curve, but I'm gradually picking up more skills.

It doesn't explain why the issue only arises on the new host's server and not on the old host - it must be something to do with the server settings.

Sometimes any errors drowses long time unnoticed in a web page and a small change in the web page like a server setting, update, move etc... can trigger it, that he is visible. The cause of such mysterious mistakes is mostly very difficult to find.