i had a multitude of these probs lol
Firstly, your CPU might be getting too hot that it reaches the auto-shutdown temperature, even with watercooled block on my CPU i still had to pump chilled air from an air conditioning unit into the watercooler's radiator lol
I used a software to check temperatures in Real-Time (as close to 'real' as possible), try this first to see just how much your CPU rises in temp when you start plotting;
Also noticed that FULL LOAD of all CPU Cores would occur but only for a minute or two before stabalising, then the temp (Full-Load) would rise again, this would repeat till the plotting was done.
Your CPU is rated for max temp of 71°C, datasheet below shows;
Also shows 4 cores and 4 threads, good info to have on hand with mining :)
Is there any way you can increase the CPU cooling, maybe up the Fan's RPM, if you have that kinda control ?
if not for CPU Fan direct, make sure an air fan (or two!) is pulling in air from the front of your computer and another air fan is taking air OUT of the back of the computer, also clean the CPU Heatsink/Re-Apply new Thermal Paste (Silicon Thermal Paste, its white, not silver/grey)
If its NOT a heat problem, it could be a HDD bad sector problem, download the manufacturer's software for your HDD and run a surface test/fix bad sectors - usually a low level check will solve the problem temporarily, when a HDD is on its way out, its on its way out :(
Try to NOT use any other HDD fixing softwares unless you got no other options, the manufacturer's usually leave behind error checking code built in on the HDD's that only their software may access, not always the case, just a rule of thumb :)
try that out, report back any changes on your progress :)