Sig 11 (segmentation violation) errors mean that the program tried to access a memory location that was not assigned or not part of its address space.  They can be either hardware errors or software flaws.  The trick is to determine which.

If it was a bug in the app, it would likely show up in many other systems running the same app.  In your case, you were successfully returning tasks right up to 16th May, after which there was a series of 88 straight errors.  My guess is that some part of the hardware (possibly RAM) failed at that point.  By the look of things, the number of errors has caused your daily task allocation to now be down to 1 per core per day.  I'm not saying it's definitely hardware - it's still possible that your system is triggering something in the app that others aren't.

If you haven't rebooted since the problem started, that would be a first step.  If errors continue, you should try replacing components, particularly RAM.  If you don't have spare RAM but you have enough installed, you could try using half the sticks, and then reverse the selection, to see if one half works but the other doesn't.  It would also be worth trying a different PSU if you had access to one.

I got interrupted whilst composing this reply.  I had started about 6 hours ago.  I've just now had another look at your tasks list and can see two successfully completed tasks returned in the meantime (?perhaps the problem is resolved?).  At least, this should have quadrupled your daily task limit.  You have no 'in progress' tasks so you should be able to get some more if you cancel any 'backoff' in communications by 'updating' the project in BOINC Manager.

Did the machine correct itself or did you mutter some magic incantation? :-).  It would be interesting to know how the problem was resolved (if in fact it really is resolved!).