Value of attribute key must specify a existing directory

I’m still trying to map a new search collection. Since the last Lucee update, I get this error message:

Value of attribute key must specify a existing directory, [ /var/www/vhosts/verkehrsverlag-online.de/httpdocs/2019/.] is invalid

But the directory does exist and it is the directory that the search should map. (The same error is displayed when I omit the “.”) - so, what is wrong?

*** When this error gets displayed, all my form entries are gone. Why?

Is there a comprehensive documentation of the search page anywhere? if so, I couldn’t find it.