Why does the Send to Proof Server task not give any information about the printing progress?
When a job is submitted to a Proof Server workflow with nesting enabled, then there is indeed no information about the printing progress returned to the Send to Proof Server task. The status jumps from Job xxx: Processing Proof... to a finished task when the nesting group in the Proof Client gets the status Printed.
This is not a desired behavior but can be explained.
Nesting creates a "virtual job" with name as "nesting" (the nesting group), which we cannot access and thus also not get feedback from. Once the virtual job is printed completely, all jobs inside it get the status Printed and feedback about these jobs is returned to the nesting group.