P.s:  I can't add subject either

Hi,

you have errors (crashes) in your pages, press F12 and see then in your browser console.

They come from your W3TC cache plugin.

NO CACHING for wpForo, you MUST exclude wpForo. You also got a warning about it when updated wpForo.

https://wpforo.com/community/faq/wpforo-and-cache-plugins

Also i would HIGHLY suggest to use an other caching plugin for the REST of your site.

<!--
Performance optimized by W3 Total Cache. Learn more:  https://www.boldgrid.com/w3-total-cache/ 

Paginacaching met disk 
Verkleind met disk
Database caching 19/198 wachtrijen in 19.000 seconden gebruikt disk (Aanvraag breed modification query)

Served from: hotrodradio.nl @ 2023-03-25 10:54:00 by W3 Total Cache
-->

Thank you, this was the problem. But we have everything filled in correctly as described. We will look for another cache cleaner.

I would highly suggest Fastest Cache or WP SUper Cache.