Cannot delete hosts after upgrade to Zabbix 4.0.4

Steps to reproduce:

1. After the Upgrade to Zabbix 4.0.4 we cannot delete hosts anymore.
   When I try to delete a (discovered) Host, i recieve the message "Cannot delete host Cannot delete host because maintenance "WUA" must contain at least one host or host group."

There IS NO maintanance by that name in our Zabbix system. The host does not have any visible connection to any maintanance.

Result:
See screenshot...
Expected:
Host is being deleted