If it "starts accessing the hard drive" it will be because your computer has run out of virtual RAM memory and has to find some more by using any available on the hard drive. What other applications were open at the time? How much RAM memory does your computer have? How full is your hard drive? When did you last do a system clean up and defrag? I think the answer may lie in those questions somewhere.

Even a reboot would help.

Or analyze the V4 morphs in stages, maybe 5 at a time?