I have been having this problem for quite some time. Only with ASIO Guard switched on though. I have just bought VEPro 5 and now the problem has completely disappeared and Cubase is the most stable I have ever had it. I wish I had bought it a long time ago and the benefits of VEPro with a DAW far outweighs the cost of buying it! Worth every penny.
I say this because I have tried everything (except for building and buying brand new Computers) to sort out the Spiking. New Operating Systems, weeks of my time installing them, installing latest drivers and Bios, EVEN bought a new GFX card just incase and nothing fixed it. It seems lots of people are having different experiences and I love Cubase so I’m not prepared to move to another DAW. Cubase + VEP = Absolutely stable. Just saying…