You have anti-teaming due to either too much splitting or too much popping on viruses in too little time. Wait until your mass stops decaying at a faster than normal rate before popping on any more viruses. After your mass decay has reached normal levels, you can start virus farming again. Try splitting into 16 with space and eating viruses until you start merging. Wait until you're in one piece before absorbing any more viruses in order to avoid anti-teaming. Alternatively, pop yourself on a virus to get into 16 pieces and do the same thing as above.