I am back :o)
After my previous ordeals I have found a new issue :o(
I assume when SpamSieve sees a message as a positive Spam message then the message is moved to the folder specified in the rule SpamSieve - Move Messages.
In my case the Junk Folder On My Computer, but strangely no Spam messages is moved, or rather no message appears there any more. A few weeks ago, I had everyday different Spam messages tree, but no longer and there are not any in any of the IMAP inboxes or in any of the IMAP Spam folders.
On my server I have disabled the junk filters to be sure its not the server who blocks.
I am going crazy?