I had a look around and it seems that the sr2sieve program gets stuck in a loop where it repeatedly exits and restarts before BOINC eventually decides to fail the task. The fact that this happens at different points in different tasks, but that they seem to occur at around the same time on the same computer points to some local issue rather than a problem with the app per se.
Did you do anything to your machines last week - I see you are running OS X Sierra, have you just upgraded? Other possible problems could include running out of disk space, your antivirus program blocking access to the BOINC directories, or similar.
Proud member of team "Aggie The Pew". Go Aggie!
3073428256125*2^1290000-1 is Prime!