I did some testing on VM somedays ago, and I noticed different behaviour on a couple of tests. At first test H.M. (aggresive mode) could block every sample that was not detected as malware, but the second time It let all undetected samples to run. Is it something that may have to do with my virtualbox session or an Avast bug or problem? 
Hardened mode is based on the cloud, so it’s either an internet issue or an avast! server issue (in the cloud).
Could probably be maintainance/downtime etc.
Thanks for replying! I know aggresive mode is based on a whitelist on Avast servers, but I hope this problem is not frequent if it’s a downtime, maintenance etc. I may retest with some samples and see what’s going on.
Some minutes ago, Hardened mode prevent taskmgr.exe to run on my real system. From the second time I try to run it, it run normally without warnings.
Similar behaviour occured some days ago when office 2013 sp1 was installed and I tried to launch office apps to see if all was ok. Avast again blocked them for one time, but from the second time all was ok.
I think Hardened mode, especially in aggresive mode, is not usable at the moment. Some say that moderate setting is more problematic but I see that both of them can cause problems.
This message may be a bit offtopic but I want to show you that something goes wrong with Hardened mode.