Webtop can't permanently delete email

I cannot permanently delete any email in WebTop 5.
If I try to delete 1 or multiple emails in the Trash folder, it asks me if am sure, and if I select ‘Yes’, nothing happens.
If I double-click an email to open it in a pop-up window, if I click the Delete button, same thing, it asks me if I am sure, and if I click ‘Yes’, nothing happens, the email stays open.
I am able to permanently delete in Roundcube, or Thunderbird.

On a side note, where could I find the WebTop log files to debug such a situation? The /var/log/webtop/webtop.log does not log anything in this situation, same with same with /var/log/maillog or messages.

That “delete” bug is solved, probably not yet published on NethServer:

https://redmine.sonicle.com/issues/161

About the log file, that depends on how the logback xml file is configured on NS7.
Neth boys can help you better here.