Since both jobs were active and already at "begin reading" stage, it means that the restore process was handed off to bptm on the media server.
Activity Monitor will show the bptm PID next to each "begin reading" entry.
You will need to look at bptm log on the media server to see what each bptm process is doing.
Level 0 log will probably not have sufficient info.
I would personally try level 3 log (Veritas Support will ask for level 5).
One more thing:
I see the following in the Data Domain Best Practice White Paper:
... “limit I/O streams per volume,” is set within a given disk pool....
This setting on the DD will limit max amount of read and write streams.
If this max limit has been reached, then maybe bpdm log on the media server will display appropriate message/entry received from DD, but this is a wild guess.
I think that DD logs may be more appropriate if this is the case.