This is still happening for me with app 37028 and definitions 12052901, and it's with com.avast.MacAvast.MAD.
Super-high CPU consumption slowing down my computer, causing my fans to run, etc. Can't use the file shield, which renders the program largely worthless.
Hallo, some badly written software (typically, USB-scanner bundled utilites etc.) might modify your filesystem repeatedly.
The fact that your fileshield's on/off state influences the overall performance of the machine is a sign of this problem.
Open ActivityMonitor, sort the processes by their CPU column, and with high probability, you will see the culprit. It's also wise to turn off avast's shields to get rid of com.avast.MacAvast.MAD activity, which is indeed great, but as a consequence only.
In the case of no succesful find, we can increase logging abilities of our shields in the next update, making such identification easier.
Regards,
pc