I've tried both 4.8 and 5 while troubleshooting this problem, using the removal tool in between and doing clean installs to see if one works where the other doesn't. The two have different interfaces and work slightly differently, so while in 4.8 it will show "VPS Destroyed" I can still tell it to update the virus database and it will replace it with a new copy, and then work for a while.
With 5, if I ask it to update the virus database when it shows the database unknown, it won't update it, telling me that avast service isn't turned on. I can have it update through add/remove programs, but this only restores it about 25% of the time.
Either way, constantly doing manual updates to get Avast running for an hour or so until it's database gets corrupted again isn't really optimal. So basically, neither 4.8 nor 5 will work, whichever one I try, the virus database somehow gets "Destroyed" after a short amount of time and then avast isn't running.