Question Forum topics with attachments

My provider MijnDomein recently moved to another platform and as a consequence my website has a malfunction in the topics with attachments. Platform is now running under PHP7.1, but same issue is under PHP5.6
Problem is that such topics will not open. After deletion of attachment the topic opens again.
Strange is that on an multiple page-topic the topic is blocked if on that window the topic with attachment is listed. On another page of that other contributions to that topic may be opened.

Looks like a php module is not set setup correct. Try the error logs to see the error.

you can try also clean all cache items.

The Joomla system has none caching as well as Kunena

Which error log do you refer to and where can I find it?

I think I found it in de Kunena errors There are lots of same error. I am not using Crypsis but the Blue eagle 1.05

The RSS issue is solved, however this one , not being able to open topics with attachments, remains.