The validation message shown on the front-end is incorrect when a Service User group on a person record has an end date added which is later than the configured SUG end date.
Currently it shows:
'Service user group '{0}' cannot have end date '{1}' later than service user group start date '{2}'.'
Whereas it should say end date in place of start date.
It is only the message that is incorrect, the validation is correct, and this usually occurs where the end date being added for a service user group on a person record is later than the end date of that service user group reference data.
This is resolved in Mosaic 22.2.1.0
In the meantime, you should be aware that the validation is correct, and the values should be amended.