Maybe you should back up your avast license file (if you use Pro/AIS) and then run the specific removal utility for avast under Windows Safe Mode. When running the removal utility, run it several times, selecting each time a different version from those you ever had in your system to remove any remnants of any version (not only remnant files but other items too).
Then manually remove any possible (hidden) files or folders that contain "avast" or "alwil" in their names.
Under Windows Normal Mode, and using an administrator account, install a clean installation of the latest stable version of avast and reboot. After the reboot, update and configure as you want / need.
Keep in mind that any item in the chest will be lost when you clean avast older installations (you can copy them to some specific backup location outside the chest before the clean up), and all configurations will be lost too (so some extra time could be needed).
If this clean up solves the problem, I'm not sure, but I guess that 240GB is worth the try.